What Is a Solo 401(k)?

Research. Education. Perspective.

Difficulty: Foundation Reading time: 19 minutes Last reviewed: August 10, 2026

> Educational Resource > > This article explains one-participant 401(k) plans and general federal retirement-plan rules. It does not recommend establishing a solo 401(k), contribution amount, Roth election, investment provider, security, loan, rollover or tax strategy for any particular person or business.

Executive Summary

A solo 401(k) is a common name for a one-participant 401(k).

The IRS also notes names such as:

• Solo-k
• Uni-k
• One-participant k^[1]

Despite the specialized marketing names, the IRS emphasizes that this is not a new type of 401(k).

It is a regular 401(k) plan covering:

• A business owner with no common-law employees, or
• The business owner and the owner's spouse.^[1]

The owner has an unusual advantage in the mechanics of the plan because the owner wears two hats:

1. Employee
2. Employer^[1]

As employee, the owner can make elective deferrals.

As employer, the business can make additional nonelective contributions.

For 2026, the basic employee elective-deferral limit is:

$24,500.^[2][3][4]

Eligible participants age 50 or older can generally make an additional:

$8,000 catch-up contribution.^[4][5]

Participants who attain ages 60, 61, 62 or 63 during 2026 can have a higher catch-up limit of:

$11,250.^[4][5]

The broader annual-additions limit for 2026 is generally:

$72,000

before eligible catch-up contributions, subject to compensation and plan rules.^[2][4]

The combination of employee and employer contribution roles can allow a self-employed person to reach the broader annual limit at a lower level of business income than an employer-only SEP contribution might permit.

But a solo 401(k) also has more plan-level administration than an IRA-based SEP.

And the word solo is important.

If the business hires common-law employees who satisfy plan eligibility requirements, the plan can no longer rely on the owner-only no-testing structure.^[1]

Key Takeaways

• A solo 401(k) is a regular 401(k) covering an owner-only business or the owner and spouse.^[1]
• The owner can contribute as both employee and employer.^[1]
• The 2026 basic elective-deferral limit is $24,500.^[2][4]
• The general 2026 age-50 catch-up is $8,000.^[4][5]
• Eligible participants ages 60 through 63 can have an $11,250 catch-up in 2026.^[4][5]
• The 2026 annual-additions limit is generally $72,000 before catch-up contributions.^[2][4]
• Compensation considered for contribution purposes is generally capped at $360,000 for 2026.^[2][4]
• Elective deferrals are generally limited by person across applicable plans.^[1][2]
• The annual-additions limit generally applies separately to plans of unrelated employers.^[2]
• Self-employed employer-contribution math requires a special calculation.^[1][6][7]
• No ordinary nondiscrimination testing is needed while the plan truly covers no common-law employees.^[1]
• If eligible employees are hired, coverage and testing obligations can arise.^[1]
• Form 5500-EZ generally becomes required when combined one-participant plan assets exceed $250,000 at year-end; a final filing is generally required when the plan terminates.^[1][8]
• Roth contributions and loans can be available if the plan document permits them.

What Does “Solo 401(k)” Mean?

“Solo 401(k)” is an industry shorthand.

The IRS uses the term one-participant 401(k).^[1]

Legally, it is simply a 401(k) plan with a very limited group of participants.

> ROIStreet Definition > > A solo 401(k) is a regular 401(k) retirement plan maintained by a business with no common-law employees other than the owner, or the owner and spouse, allowing the owner to contribute in both employee and employer capacities.

Who Can Use a Solo 401(k)?

The core structure is designed for a business that has:

• An owner, and
• No common-law employees who must be covered

or:

• An owner
• The owner's spouse working in the business
• No other common-law employees who must be covered.^[1]

Business form can include structures such as:

• Sole proprietorship
• Partnership
• LLC
• S corporation
• C corporation

The contribution calculation can differ by tax structure.

The Business Must Be Real

A 401(k) plan is an employer retirement plan.

A person generally needs earned income or compensation from a trade or business to support plan contributions.

Portfolio income by itself—such as ordinary investment dividends or capital gains—does not automatically create self-employment compensation for a solo 401(k).

The business and compensation structure matter.

Can a Spouse Participate?

Yes, when the spouse actually works for the business and receives qualifying compensation or earned income under the applicable structure.

The IRS specifically describes a one-participant plan as potentially covering the owner and spouse.^[1]

Marriage alone does not create contribution capacity.

The spouse must have a legitimate compensation relationship with the business.

When both spouses qualify, each can potentially have:

• Their own employee elective deferral
• An employer contribution based on their own eligible compensation

subject to annual limits.

Why the Owner Has “Two Hats”

The IRS explains that the owner contributes in two capacities.^[1]

Hat 1: Employee

The owner can make an elective deferral.

Hat 2: Employer

The business can make a nonelective employer contribution.

Those two layers are one of the defining mechanics of a solo 401(k).

2026 Employee Elective-Deferral Limit

For 2026, the employee elective-deferral limit is:

$24,500.^[2][3][4]

The contribution can generally be up to 100% of eligible compensation or earned income if compensation is lower than the dollar limit.^[1]

The actual plan must permit the deferral.

2026 Catch-Up Contributions

Eligible participants age 50 or older can generally make a catch-up contribution beyond the ordinary elective-deferral limit.

For 2026:

$8,000.^[4][5]

That can make total employee elective deferrals:

$24,500 + $8,000 = $32,500

for an otherwise eligible participant.

Higher Catch-Up for Ages 60 Through 63

SECURE 2.0 created a higher catch-up for participants attaining ages 60, 61, 62 or 63 during the calendar year.

For 2026:

$11,250.^[4][5]

That can make total employee elective deferrals:

$24,500 + $11,250 = $35,750

subject to compensation and plan terms.

The $11,250 replaces the ordinary $8,000 catch-up for that participant and year; the two amounts are not stacked.

2026 Roth Catch-Up Rule

Beginning in 2026, applicable employer plans with Roth features are subject to a new catch-up rule for certain higher-wage participants.

IRS guidance states that catch-up contributions generally must be made on a Roth basis when the participant's prior-year wages from the sponsoring employer exceed:

$150,000 for 2026.^[4][5]

The rule is based on statutory wage concepts and can be more nuanced for self-employed owners who do not receive wages in the same manner as ordinary employees.

Business owners affected by catch-up contributions should verify the rule with the plan administrator and current IRS guidance.

Employer Nonelective Contributions

The second contribution layer comes from the business.

IRS guidance states that employer nonelective contributions can generally be up to:

25% of compensation

for an employee, subject to the broader annual limits.^[1]

For a self-employed individual such as a sole proprietor or partner, the calculation is different because compensation is based on adjusted net earnings from self-employment.^[1][6][7]

2026 Annual-Additions Limit

The combined annual additions to a participant's account generally include:

• Employee elective deferrals
• Employer contributions
• Certain after-tax employee contributions if the plan permits them

For 2026, the annual-additions ceiling is generally:

$72,000.^[2][4]

Eligible catch-up contributions can be made above this ceiling.^[1][2]

Catch-Ups Sit Outside the $72,000 Ceiling

This distinction matters.

For an eligible participant age 50 or older, the 2026 $72,000 annual-additions limit does not include eligible catch-up contributions.^[1][2]

That means potential total contributions can exceed $72,000 where:

• Compensation supports the contribution
• The plan permits the contribution
• The participant is catch-up eligible
• All other limits are satisfied

For example, a qualifying participant using the general $8,000 catch-up could potentially reach:

$80,000

in total plan contributions for 2026.

A qualifying age-60-through-63 participant could potentially reach:

$83,250

using the $11,250 catch-up.

These are ceilings, not automatic contribution amounts.

2026 Compensation Limit

For 2026, compensation considered for plan contribution purposes is generally capped at:

$360,000.^[2][4]

The compensation limit can affect employer contribution calculations.

A plan cannot simply apply its employer percentage to unlimited compensation.

Employee Limit vs. Total Plan Limit

It is useful to separate three numbers:

$24,500

Basic 2026 employee elective-deferral limit.

$72,000

2026 annual-additions limit before catch-up.

$360,000

2026 compensation cap used for applicable plan calculations.

These numbers answer different questions.

Example: Owner Under Age 50

Suppose an incorporated business owner has $120,000 of eligible W-2 compensation.

Employee elective deferral:

$24,500

Potential employer contribution at 25%:

$30,000

Total:

$54,500

This simplified example is below the $72,000 annual-additions limit.

It ignores taxes, plan-specific compensation definitions and any other retirement-plan contributions.

Example: Owner Reaches the Annual Limit

Suppose an incorporated owner has sufficient eligible W-2 compensation to support:

Employee deferral:

$24,500

Employer contribution:

$47,500

Total:

$72,000

The annual-additions ceiling has been reached before any eligible catch-up contribution.

The employer contribution is not automatically $47,500; compensation must support it under the plan's formula.

Why Self-Employed Math Is Different

For a sole proprietor or partner, the employer contribution is not calculated by simply multiplying Schedule C profit or partnership self-employment earnings by 25%.

IRS guidance says the self-employed calculation uses earned income after deducting:

• One-half of self-employment tax
• The owner's own retirement-plan contribution.^[1][6]

That creates a circular calculation.

Publication 560 provides worksheets and rate tables.^[7]

The Reduced Contribution Rate

As with a SEP, a plan formula stated as 25% of employee compensation generally translates to a reduced effective rate when determining the self-employed owner's own employer contribution.

The owner's exact contribution depends on adjusted net earnings from self-employment.

The key rule for readers is:

Do not multiply Schedule C profit by 25% and assume the answer is the allowable employer contribution.

S Corporation Owner Compensation

The IRS states that an S corporation shareholder-employee uses Form W-2 compensation to support 401(k) salary deferrals and employer contributions.^[9]

S corporation shareholder distributions are not automatically retirement-plan compensation.

That distinction can materially affect the amount that can be contributed.

Employee Deferral Limit Follows the Person

Suppose a business owner also has a day job with another employer.

The person participates in:

• Employer A's 401(k)
• The person's solo 401(k) through Business B

The IRS states that the elective-deferral limit is by person, not by plan.^[1]

The owner does not receive a fresh $24,500 employee-deferral limit merely because there are two unrelated 401(k) plans.

Example: Day Job Plus Solo 401(k)

Assume a person under age 50 contributes:

$20,000

to a day-job 401(k) in 2026.

The remaining basic elective-deferral capacity across applicable 401(k) plans would generally be:

$24,500 − $20,000 = $4,500

The person may still have separate employer-contribution capacity in the solo 401(k), depending on business income and the annual-additions rules.

Annual-Additions Limit Can Be Plan-Specific

IRS guidance provides an important contrast.

While the elective-deferral limit follows the individual, the Section 415 annual-additions limit generally applies separately to plans maintained by unrelated employers.^[2]

This means an owner who maxed the employee deferral at a day job can still potentially make employer contributions to an unrelated solo 401(k), subject to the solo plan's own annual-additions limit and business compensation.

This is a technical but important distinction.

Related Employers Can Change the Analysis

The separate-plan annual-additions concept depends on whether employers are legally treated as unrelated.

Controlled-group and affiliated-service-group rules can cause nominally separate businesses to be treated together for retirement-plan purposes.

A business owner should not assume that two legal entities automatically create independent contribution limits.

This is an area where retirement-plan or tax counsel can be important.

Traditional 401(k) Contributions

A solo 401(k) can permit traditional elective deferrals.

Traditional deferrals generally reduce current federal taxable income from the deferred compensation, subject to applicable tax rules.

The contribution and earnings generally become taxable when distributed.

This is tax deferral, not tax elimination.

Roth Solo 401(k) Contributions

A plan can also permit designated Roth elective deferrals.

Roth employee deferrals are made with after-tax dollars.

Qualified Roth distributions can generally be tax-free under applicable rules.

The plan document and provider must support a Roth feature.

The word solo does not automatically mean Roth is available.

Traditional vs. Roth Elective Deferrals

The tax election does not change the underlying investment risk.

Roth Does Not Double the Employee Limit

If an owner contributes in 2026:

• $12,500 traditional
• $12,000 Roth

total employee elective deferrals are:

$24,500

The basic 2026 limit has been reached.

Traditional and Roth contributions share the same employee-deferral ceiling.

Employer Contributions

A solo 401(k) can also receive employer contributions.

Historically, employer nonelective contributions were typically made on a pre-tax basis.

SECURE 2.0 permits plans to offer Roth treatment for certain employer matching or nonelective contributions under applicable requirements.

Availability is plan-specific and tax reporting is more technical.

A participant should not assume every solo 401(k) provider supports Roth employer contributions.

After-Tax Contributions

Some 401(k) plan documents can permit employee after-tax contributions that are neither traditional elective deferrals nor designated Roth elective deferrals.

These can interact with the $72,000 annual-additions limit.

Provider support and plan design vary widely.

Because the mechanics can become complex—particularly when combined with Roth conversion features—after-tax contributions should be treated as an advanced plan-design topic rather than a standard feature of every solo 401(k).

Why a Solo 401(k) Can Out-Contribute a SEP at Lower Income

A SEP generally relies on the employer contribution formula.

A solo 401(k) can combine:

• Employee elective deferral
• Employer contribution

That employee layer can allow a larger total contribution at certain income levels.

Simplified conceptual comparison

A business owner with moderate income might be able to contribute:

• A full or substantial employee deferral
• Plus an employer contribution

to the solo 401(k).

A SEP owner contribution at the same income depends primarily on the employer percentage.

At high enough compensation, both plans can reach the same general defined-contribution dollar ceiling.

No Ordinary Nondiscrimination Testing While Truly Solo

The IRS states that a business owner with no common-law employees does not need to perform ordinary nondiscrimination testing because there are no employees who could receive disparate benefits.^[1]

This is one reason owner-only plans can be simpler than larger 401(k) plans.

But the no-testing advantage depends on the participant population.

What Happens When Employees Are Hired?

The IRS is explicit:

If the employer hires common-law employees and those employees meet the plan's eligibility requirements, they generally must be included.^[1]

At that point:

• Nondiscrimination testing can apply
• Safe-harbor design may become relevant
• Employer contributions may need to cover employees
• Plan administration becomes more complex

The marketing label “solo 401(k)” does not override federal coverage rules.

Common-Law Employee Is the Key Concept

A business owner cannot preserve solo status merely by calling every worker an independent contractor.

Worker classification follows federal law.

If a worker is legally a common-law employee and satisfies the plan's eligibility requirements, the plan may have coverage obligations.

Misclassification can create both employment-tax and retirement-plan problems.

Spouse Is Different From an Unrelated Employee

The IRS specifically permits a one-participant 401(k) to cover:

• Owner only, or
• Owner and spouse.^[1]

A spouse working in the business does not, by itself, destroy one-participant-plan status.

An unrelated eligible common-law employee can.

Investment Choices

Solo 401(k) investment options depend on:

• Plan document
• Trustee or custodian
• Brokerage platform
• Provider rules

Potential investments can include:

• Stocks
• Bonds
• ETFs
• Mutual funds
• CDs
• Cash
• Other permitted investments

Some specialized plans allow broader self-directed assets.

The 401(k) tax wrapper does not guarantee any investment.

Self-Directed Solo 401(k)s

Some providers market self-directed solo 401(k)s with broader asset access.

Possible investments can include:

• Real estate
• Private investments
• Certain precious metals
• Other legally permitted assets

These structures can involve significant:

• Prohibited-transaction risk
• Valuation complexity
• Custody issues
• Tax-reporting requirements
• Fraud risk
• Illiquidity

The fact that a plan document permits an asset does not make the asset economically sound.

Prohibited Transactions

Qualified retirement plans are subject to prohibited-transaction and self-dealing rules.

A business owner controlling the plan must distinguish:

• Plan assets
• Personal assets
• Business assets

Using retirement-plan property for personal benefit can create serious tax consequences.

Alternative investments can make those boundaries less intuitive.

Professional legal and tax guidance can be important.

Can a Solo 401(k) Permit Loans?

A 401(k) plan can be designed to permit participant loans.

That includes a one-participant 401(k) if the plan document allows the feature.

Federal rules generally limit a qualified plan loan to the lesser of:

• 50% of the participant's vested account balance, or
• $50,000

subject to applicable exceptions and prior-loan adjustments.

An owner should not assume that a brokerage account labeled “solo 401(k)” automatically includes a loan feature.

The plan document controls.

Loan Risks

A compliant 401(k) loan is not the same as a taxable withdrawal.

But it can still create economic risks:

• Money removed from investments can miss market gains
• Repayment creates cash-flow obligations
• Loan fees can apply
• Failure to follow repayment rules can create a deemed distribution
• Business or plan termination can complicate repayment

The phrase “borrowing from yourself” does not eliminate these costs.

Hardship Distributions

A solo 401(k) can potentially include hardship-distribution provisions if the plan document permits them and federal requirements are satisfied.

A hardship distribution is different from a loan.

It is generally not repaid to the plan.

The distribution can:

• Reduce retirement assets permanently
• Create income tax
• Potentially trigger an additional early-distribution tax

depending on the participant's circumstances and source of funds.

When Can Money Be Distributed?

401(k) distribution rules depend on the plan document and federal law.

Possible distributable events can include:

• Reaching a permitted age
• Separation from service
• Disability
• Plan termination
• Hardship where the plan allows it
• Other qualifying events

A solo 401(k) is not a general checking account simply because the owner controls the business and serves as plan administrator.

The plan must follow retirement-plan distribution rules.

Early Distributions

Taxable distributions before age 59½ can generally be subject to a 10% additional federal tax unless an exception applies.

This differs from the general early-distribution treatment of governmental 457(b) plans.

A business owner should distinguish:

• Legal availability of a distribution
• Ordinary income-tax treatment
• Additional early-distribution tax

These are separate questions.

Required Minimum Distributions

Pre-tax solo 401(k) balances are generally subject to required minimum distribution rules.

The applicable starting age depends on current federal law and the participant's birth year.

Employer plans can have a still-working exception in some circumstances, but owner status can limit that exception.

For an owner-only business, the RMD rules should be reviewed directly rather than assuming the ordinary employee still-working exception applies.

Roth 401(k) Lifetime RMDs

Under current federal law, designated Roth accounts in employer plans generally no longer require lifetime RMDs for the original owner.

That aligns Roth 401(k) lifetime RMD treatment more closely with Roth IRAs.

Beneficiary distribution rules still apply after death.

The absence of lifetime Roth RMDs does not mean every Roth distribution is automatically tax-free.

Qualified-distribution rules still matter.

Rollovers

Eligible solo 401(k) distributions can generally be rolled to another eligible retirement arrangement, depending on source and destination.

Possible destinations can include:

• Traditional IRA
• Another 401(k)
• 403(b)
• Governmental 457(b)
• Roth IRA in a transaction that can create taxable conversion income
• Another designated Roth account for qualifying Roth assets

A direct rollover can generally avoid current taxation on eligible pre-tax amounts.

The destination can change:

• Investment choices
• Fees
• Creditor protection
• Withdrawal rules
• Loan availability
• Administrative requirements

A rollover is therefore more than an investment transfer.

Rolling Money Into a Solo 401(k)

A solo 401(k) can also potentially accept eligible incoming rollovers if the plan document permits them.

Possible sources can include certain:

• Traditional IRAs
• SEP-IRAs
• 401(k)s
• 403(b)s
• Governmental 457(b)s

Roth IRA money generally cannot be rolled into a designated Roth 401(k) under ordinary federal rollover rules.

Provider rules also matter.

Why Incoming Rollovers Can Matter

A business owner might evaluate incoming rollovers for reasons such as:

• Consolidating retirement accounts
• Accessing plan investment options
• Changing IRA balances that affect certain Roth-conversion calculations
• Maintaining plan-level protections

But rollovers can also give up benefits associated with the source account.

The tax and legal tradeoffs should be reviewed before moving assets.

Creditor Protection

Qualified 401(k) plans can receive federal creditor protections that differ from those applicable to IRAs.

The exact protection can depend on:

• ERISA status
• Bankruptcy law
• State law
• Plan structure
• Nature of the claim

A one-participant plan can have legal characteristics different from a conventional employer plan covering rank-and-file employees.

Creditor-protection analysis is legal and fact-specific.

It should not be reduced to a blanket claim that one account is always “more protected.”

Form 5500-EZ

A solo 401(k) can have an annual federal filing requirement.

The IRS states that a one-participant plan generally must file Form 5500-EZ when total one-participant plan assets exceed:

$250,000 at the end of the plan year.^[1][8]

The threshold is based on the employer's combined one-participant plan assets, not necessarily each individual plan viewed in isolation.

The $250,000 Rule Is Aggregated

Suppose an employer maintains two one-participant retirement plans.

Plan A assets:

$180,000

Plan B assets:

$90,000

Combined:

$270,000

The employer cannot necessarily avoid filing merely because each separate plan is below $250,000.

Current Form 5500-EZ instructions require aggregation of the employer's one-participant plan assets when applying the threshold.

Final Return Required

The IRS also states that a final return/report generally must be filed when a one-participant plan is terminated, regardless of plan asset value.^[8]

This is an important exception to the ordinary asset-based filing relief.

A business owner should not assume:

“My plan is under $250,000, so I never file.”

Termination changes the rule.

Form 5500-SF Alternative

A one-participant plan can generally have the option to file Form 5500-SF electronically instead of paper Form 5500-EZ when the applicable requirements are satisfied.^[7]

The mechanics and filing system differ.

The relevant point for investors is that the plan can develop a federal reporting obligation even though it has only one owner-participant.

Why Filing Errors Matter

Late or missing retirement-plan returns can create penalties.

The IRS offers certain relief procedures for delinquent Form 5500-EZ filers.

The better approach is to monitor the filing threshold annually and recognize when the plan reaches it.

Assets can cross $250,000 because of:

• New contributions
• Investment growth
• Incoming rollovers

not merely because the owner intentionally contributed more.

Plan Administration

A solo 401(k) is simpler than a multi-employee 401(k) in some respects.

But it still requires a valid plan.

Administrative tasks can include:

• Maintaining the plan document
• Following contribution elections
• Calculating employer contributions
• Tracking Roth and traditional sources
• Processing distributions correctly
• Monitoring loan rules if loans are offered
• Updating beneficiaries
• Filing Form 5500-EZ or Form 5500-SF when required
• Adopting required plan amendments

“Solo” does not mean “no administration.”

Contribution Timing

Contribution deadlines can differ by:

• Business type
• Employee vs. employer contribution
• Tax year
• Plan establishment date
• Election timing

A corporation using W-2 payroll operates differently from a sole proprietor reporting self-employment income.

The tax law has also changed in recent years regarding establishment timing for certain owner-only plans.

For that reason, a general article should not reduce contribution timing to one universal date.

The plan provider and current IRS guidance should be checked for the specific business form and year.

Employee Deferral Elections Matter

An elective deferral is not simply an employer contribution relabeled after year-end.

The plan must comply with applicable election and plan-document rules.

This can be particularly important for:

• S corporation owners
• C corporation owners
• Partnerships
• Sole proprietors

The exact deadline and documentation depend on plan and tax structure.

Solo 401(k) and a Spouse

When both spouses work in the business and receive qualifying compensation, the plan can potentially cover both while remaining a one-participant plan for IRS reporting terminology.^[1]

Each spouse can have separate contribution limits tied to their own compensation.

For example, each spouse can potentially have:

• Their own employee elective deferral
• Their own employer contribution

subject to overall plan and compensation limits.

The business cannot create spouse contribution capacity without actual eligible compensation.

Example: Owner and Spouse

Assume both spouses work for an incorporated business and each receives $100,000 of eligible W-2 compensation.

Each could potentially make an employee elective deferral up to the applicable personal limit.

The corporation could also make employer contributions based on each spouse's compensation.

The exact maximum depends on:

• Age
• Other plan deferrals
• Compensation
• Plan document
• Annual-additions limits

The spouse's participation can materially increase total household retirement-plan contributions because each person is a separate participant.

Solo 401(k) vs. SEP IRA

These two structures are among the most common self-employed retirement plans.

Neither structure is universally better.

Why a SEP Can Be Simpler

A SEP generally uses IRA accounts and can have:

• Less plan administration
• No ordinary annual Form 5500
• Relatively simple employer contribution mechanics

For an owner-only business with high enough income to reach the same desired contribution, that simplicity can be meaningful.

But a SEP lacks the employee deferral and catch-up structure of a solo 401(k).

Why a Solo 401(k) Can Be More Flexible

A solo 401(k) can provide features such as:

• Employee elective deferrals
• Catch-up contributions
• Roth elective deferrals
• Potential plan loans
• Potential after-tax contributions depending on document
• Employer contributions

That flexibility comes with more plan administration.

The correct comparison is therefore:

contribution mechanics + plan features + administration + business workforce

not merely the maximum headline number.

Solo 401(k) vs. SIMPLE IRA

A SIMPLE IRA can fit a business wanting employee payroll deferrals with a standardized employer contribution.

A solo 401(k) is built around an owner-only participant population.

Solo 401(k) vs. Traditional IRA

A solo 401(k) is an employer retirement plan.

A traditional IRA is an individual retirement account.

For 2026:

Solo 401(k) basic employee deferral:

$24,500

Regular IRA contribution limit:

$7,500

or:

$8,600 age 50+

The contribution systems are separate.

A person can potentially contribute to both if eligible, although workplace-plan participation can affect the deductibility of a traditional IRA contribution.

Solo 401(k) and Regular Roth IRA

A business owner participating in a solo 401(k) can potentially also make a regular Roth IRA contribution if eligible under Roth IRA income rules.

The solo 401(k) Roth election does not use the ordinary Roth IRA contribution limit.

They are separate statutory contribution systems.

However, income limits apply to direct regular Roth IRA contributions, while designated Roth 401(k) elective deferrals do not use the same income-eligibility ceiling.

Investment Fees

Solo 401(k) costs can include:

• Plan setup fees
• Annual administration fees
• Brokerage fees
• Fund expense ratios
• Advisory fees
• Loan fees
• Self-directed asset fees
• Form 5500-EZ preparation fees

Some brokerage providers charge little or no direct plan fee.

Others provide more plan features for a higher cost.

The lowest price does not necessarily include the same:

• Roth features
• Loan provisions
• After-tax contributions
• Self-directed investments
• Administrative support

Feature comparison should accompany fee comparison.

Beneficiary Designations

A solo 401(k) should have beneficiary designations.

Spousal rights can apply under qualified-plan rules depending on plan design and applicable law.

The beneficiary form can affect how retirement assets pass after death.

It should be reviewed after:

• Marriage
• Divorce
• Death in the family
• Estate-plan changes

Beneficiary designations should not be assumed to update automatically through a will.

Common Plan Errors

Potential one-participant 401(k) mistakes can include:

• Exceeding the personal elective-deferral limit across multiple plans
• Miscalculating self-employed compensation
• Treating S corporation distributions as plan compensation
• Missing an eligible common-law employee
• Failing to file Form 5500-EZ
• Using a plan feature not actually contained in the plan document
• Taking an improper participant loan
• Making prohibited transactions with plan assets
• Failing to adopt required plan amendments

The solo structure reduces some complexity.

It does not remove qualification requirements.

Common Misconceptions

"A solo 401(k) is a special kind of IRA."

No. The IRS says it is a regular 401(k) plan with one business owner participant, or owner and spouse.^[1]

"I get $24,500 at my day job and another $24,500 in my solo plan."

Not generally. The elective-deferral limit follows the individual across applicable 401(k) plans.^[1][2]

"The $72,000 limit includes catch-up contributions."

No. Eligible catch-up contributions can generally be made above the annual-additions ceiling.^[1][2]

"I can contribute 25% of my Schedule C profit as employer contribution."

Not generally. Self-employed contribution calculations require adjustments and a special computation.^[1][6]

"If I hire employees, I can just keep calling it a solo 401(k)."

The name does not override coverage rules. Eligible common-law employees can have to be included and testing can apply.^[1]

"My spouse can contribute because we're married."

The spouse generally needs qualifying work and compensation from the business.

"Every solo 401(k) has Roth and loans."

No. Those features must be supported by the plan document and provider.

"A solo 401(k) never files Form 5500."

False. The annual filing generally applies once aggregate one-participant plan assets exceed $250,000, and a final filing generally applies on termination.^[1][8]

"A solo 401(k) is always better than a SEP."

No. Contribution goals, business income, age, employees, plan features and administrative burden can change the comparison.

"The investments are safer because the account is a 401(k)."

No. Tax treatment does not protect against market losses.

Frequently Asked Questions

What is a solo 401(k) in simple terms?

It is a regular 401(k) plan covering a business owner with no common-law employees, or the owner and spouse.^[1]

What is the 2026 employee contribution limit?

The basic elective-deferral limit is $24,500.^[2][3][4]

What is the 2026 age-50 catch-up?

The general catch-up is $8,000.^[4][5]

What is the 2026 age-60-through-63 catch-up?

The higher catch-up is $11,250.^[4][5]

What is the 2026 total solo 401(k) contribution limit?

Annual additions generally cannot exceed $72,000 before eligible catch-up contributions, subject to compensation and plan rules.^[2][4]

Can total contributions exceed $72,000?

Yes, where an eligible participant makes permitted catch-up contributions. Catch-up amounts generally sit outside the annual-additions limit.^[1][2]

Can a spouse participate?

Yes, if the spouse works for the business and has qualifying compensation or earned income.^[1]

Can I have a solo 401(k) and a day-job 401(k)?

Yes, but the employee elective-deferral limit generally applies across the plans by person.^[1][2]

Can I still make an employer contribution if I already maxed my day-job 401(k)?

Potentially. Employer contributions to an unrelated solo plan are analyzed under the solo plan's compensation and annual-additions rules.^[2]

Can a sole proprietor simply use 25% of Schedule C profit?

No. The IRS requires a special self-employed contribution calculation.^[1][6][7]

Can an S corporation owner use distributions to fund the contribution limit?

The IRS states that 401(k) contribution calculations for an S corporation shareholder-employee are based on Form W-2 compensation, not shareholder distributions.^[9]

Can a solo 401(k) have Roth contributions?

Yes, if the plan document permits designated Roth contributions.

Can a solo 401(k) have a loan feature?

Yes, if the plan permits loans and federal loan rules are followed.

What happens if I hire an employee?

If a common-law employee satisfies plan eligibility requirements, the employee generally must be included and the plan can become subject to ordinary coverage and nondiscrimination requirements.^[1]

When is Form 5500-EZ required?

A one-participant plan generally must file when aggregate one-participant plan assets exceed $250,000 at year-end. A final return is generally required when the plan is terminated.^[1][8]

Is a solo 401(k) better than a SEP IRA?

Neither is universally better. A solo 401(k) can provide employee deferrals, catch-ups and more plan features, while a SEP can be administratively simpler.

2026 Solo 401(k) Rules at a Glance

Annual dollar limits can change with inflation.

A Solo 401(k) Research Framework

Before establishing or reviewing a one-participant 401(k), useful questions include:

1. Does the business have any common-law employees?
2. Does the spouse work in the business?
3. What is the business tax structure?
4. What is each participant's eligible compensation or earned income?
5. Does the owner contribute to another employer 401(k) or 403(b)?
6. How much personal elective-deferral capacity remains?
7. What employer contribution can the business support?
8. Does the $72,000 annual-additions limit apply before catch-up?
9. Does an age-based catch-up apply?
10. Does the 2026 Roth catch-up rule affect the participant?
11. Does the plan offer traditional and Roth deferrals?
12. Does it permit Roth employer contributions?
13. Does it permit after-tax contributions?
14. Does it permit participant loans?
15. What investments are available?
16. What plan, brokerage and investment fees apply?
17. Are self-directed assets being considered?
18. Could prohibited-transaction rules become relevant?
19. Are aggregate one-participant plan assets approaching $250,000?
20. Has Form 5500-EZ or Form 5500-SF become required?
21. Could a future employee hire change coverage and testing obligations?
22. How does the plan compare with a SEP or SIMPLE IRA for this workforce?

These questions organize the plan analysis without determining which retirement plan, contribution amount, investment or tax election is appropriate for a particular business owner.

The Bottom Line

A solo 401(k) is not a special loophole or a unique retirement-account species.

It is a regular 401(k) plan used by an owner-only business—or an owner and spouse—with no other common-law employees who must be covered.^[1]

Its defining contribution feature is that the owner can act as both:

• Employee
• Employer

For 2026, the basic employee elective-deferral limit is:

$24,500.^[2][4]

The broader annual-additions limit is:

$72,000 before eligible catch-up contributions.^[2][4]

Eligible participants age 50 or older can generally add an $8,000 catch-up, while eligible participants attaining ages 60 through 63 can have an $11,250 catch-up.^[4][5]

But the headline limits can obscure the real analysis.

A solo 401(k) also requires attention to:

• Business compensation
• Other employer plans
• Self-employed contribution math
• Plan-document features
• Roth treatment
• Loans
• Investment choices
• Employee hiring
• Form 5500-EZ filing
• Ongoing plan administration

The useful question is not simply:

"How much can I contribute?"

It is:

"What part of the contribution comes from the employee role, what part comes from the employer role, what other plans and compensation affect the limits, and will this business remain owner-only long enough for the one-participant structure to continue working as intended?"

That is the foundation for understanding a solo 401(k) as an employer retirement plan rather than merely a high-limit savings account.

Continue Your Learning

1. What Is a SEP IRA? — Compare an employer-only IRA-based structure with the employee-and-employer solo 401(k).
2. What Is a SIMPLE IRA? — Compare the solo structure with a small-employer plan designed for employee salary deferrals.
3. What Is a 401(k)? — Understand the broader plan rules underlying every one-participant 401(k).
4. What Is an IRA? — Compare individual retirement accounts with employer qualified plans.
5. What Is a Brokerage Account? — Understand the custody layer underlying many retirement investments.
6. What Is a Target-Date Fund? — Learn about an investment that can be held inside a solo 401(k).
7. What Is Asset Allocation? — Separate plan contribution mechanics from portfolio construction.
8. Risk vs. Return Explained — Understand why retirement tax advantages do not eliminate investment risk.

Sources & References

1. Internal Revenue Service: One-Participant 401(k) Plans
2. Internal Revenue Service: 401(k) and Profit-Sharing Plan Contribution Limits
3. Internal Revenue Service: 401(k) Limit Increases to $24,500 for 2026
4. Internal Revenue Service: Notice 2025-67 — 2026 Retirement Plan Cost-of-Living Adjustments
5. Internal Revenue Service: Retirement Topics — Catch-Up Contributions
6. Internal Revenue Service: Calculating Your Own Retirement Plan Contribution and Deduction
7. Internal Revenue Service: Publication 560 — Retirement Plans for Small Business
8. Internal Revenue Service: Operating a 401(k) Plan
9. Internal Revenue Service: Retirement Plan FAQs Regarding Contributions — S Corporation
10. U.S. Securities and Exchange Commission — Investor.gov: 401(k) Plans

Educational Disclaimer

ROIStreet publishes educational content intended to help readers better understand investing, retirement plans, self-employed retirement accounts and related financial topics.

Nothing in this article should be interpreted as personalized investment, legal, tax or financial advice, or as a recommendation to establish, terminate, amend, fund or select a solo 401(k), SEP, SIMPLE IRA, Roth feature, loan provision, investment provider, security, rollover or contribution strategy.

One-participant 401(k) rules depend on business structure, compensation, employee status, plan documents, contribution elections, other retirement plans and current federal law. Business owners should review current IRS and plan information and consult qualified tax, legal, retirement-plan or financial professionals where appropriate.

The ROIStreet Reader Promise

We strive to explain before we evaluate, present evidence before opinions, discuss risks alongside potential benefits, distinguish facts from analysis, and correct material errors transparently.

Our purpose is to help readers better understand investing—not to tell them what to do.