Investing Basics

Days Inventory Outstanding

Days inventory outstanding estimates the average number of days inventory remains on hand before sale or use. A common formula divides average inventory by average daily cost of sales.

Updated 2026-09-02 · Foundation

Formula

DIO = Average inventory ÷ Average daily cost of sales

Assume:

average inventory: $240 million
quarterly cost of sales: $360 million
quarter length: 90 days

Average daily COGS:

$4 million

DIO:

60 days

The company carries inventory equal to roughly 60 days of cost of sales.

DIO and inventory turnover

Inventory turnover uses:

COGS ÷ Average inventory

DIO expresses the same relationship in days.

If annual inventory turnover is:

approximate inventory days are:

365 ÷ 6 ≈ 61 days

Higher turnover generally means lower DIO.

Lower DIO can release cash

Suppose DIO falls:

75 days → 55 days

while sales remain stable.

The company needs less inventory to support the same level of activity.

That can:

release working capital
improve operating cash flow
reduce storage cost
lower obsolescence risk

When customer service and margins remain intact, this is usually a high-quality improvement.

Lower DIO can also create stockouts

A company can cut inventory too aggressively.

DIO improves.

But customers begin facing:

unavailable products
shipment delays
lost orders
rush freight

The ratio looks better while service quality deteriorates.

The goal is not the lowest possible DIO.

It is the lowest inventory level that still supports the business reliably.

Rising DIO can signal weak demand

If inventory rises while COGS is flat or falling, DIO increases.

Possible causes include:

overordering
slowing demand
obsolete product
poor forecasting
launch delays

That can tie up cash and increase markdown risk.

Rising DIO can be strategic

Companies sometimes carry extra inventory because of:

supply-chain disruption
tariff risk
long supplier lead times
expected demand
new product launches
seasonal preparation

The higher DIO still uses cash.

The decision can be rational if the inventory protects profitable sales.

Donaldson's formula

Donaldson states that it calculates DIO by dividing average inventory for the quarter by average cost of goods sold per day for the same quarter.^[2]

That is a well-matched formula:

balance-sheet average in the numerator
daily cost flow in the denominator

CDW example

CDW reported days of supply in inventory of 16 days at June 30, 2026 versus 13 days a year earlier. The company attributed the increase partly to higher average customer stocking positions and increased hardware cost.^[1]

That example matters because rising inventory days were not described simply as weak demand.

Business mix and cost changes can affect the ratio.

Church & Dwight example

Church & Dwight reported DIO of 63 days for the quarter ended June 30, 2026, down from 69 days a year earlier. The company linked the decline to inventory-management initiatives.^[3]

The lower DIO contributed to a shorter cash conversion cycle.

This is where the metric often becomes most useful: inside the broader working-capital system.

Seasonality can dominate the number

A retailer may build inventory months before peak demand.

DIO rises before the selling season.

After the peak:

inventory falls
COGS rises
DIO drops

Comparing an off-season quarter with a peak-season quarter can create a false conclusion.

Same-quarter year-over-year comparisons are usually stronger.

Product mix matters

A distributor can sell:

fast-moving consumables
slower specialized equipment

If business mix shifts toward specialized products, consolidated DIO can rise.

That may reflect the product mix rather than poorer management.

Segment data can be more informative than one company-wide ratio.

Markdown-driven improvement can be low quality

A retailer can clear excess inventory with aggressive discounts.

Inventory falls.

DIO improves.

Gross margin falls.

The cash release may be necessary.

It is not automatically a better economic outcome.

ROIStreet’s GLS-049 — Gross Margin provides the profitability context.

Acquisitions can distort DIO

A late-quarter acquisition can add a full inventory balance immediately.

Only part of the acquired cost of sales may be included in the period.

DIO can rise mechanically.

Post-acquisition ratios often need normalization.

Inflation can move the ratio

Higher input prices increase:

inventory carrying values
cost of sales

Those changes do not necessarily happen at the same time.

During rapid inflation, DIO can move even if physical unit turnover changes less.

The ratio remains useful but is not a pure unit measure.

Very high DIO increases obsolescence risk

Long holding periods expose inventory to:

technology changes
fashion shifts
spoilage
damage
price declines
storage costs

The risk matters most in electronics, apparel and other short-life products.

High DIO deserves deeper inventory-quality analysis.

Very low DIO can be structurally normal

Some companies operate with:

just-in-time replenishment
drop shipping
vendor-managed inventory
short production cycles

Low inventory days can be efficient.

The trade-off is greater exposure to supplier disruption.

DIO and cash flow

Higher DIO generally means more cash is tied up in inventory.

Lower DIO generally releases cash.

The relationship can be obscured by acquisitions, foreign exchange and write-downs, but over time inventory days and operating cash flow should tell a coherent story.

Example

Average inventory of $240 million divided by average daily COGS of $4 million produces DIO of 60 days. If inventory rises to $320 million with COGS unchanged, DIO rises to 80 days.

Professional note

A useful DIO review asks:

Demand: Is inventory growing faster than sales?
Margin: Are markdowns driving faster turnover?
Service: Are stockouts increasing?
Seasonality: Is the reporting date normal?
Supply: Are longer lead times forcing safety stock?
Cash: How much operating cash is tied up in inventory?

DIO is most useful when it measures inventory efficiency without rewarding a company for carrying too little product to serve customers properly.

Related terms

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The Absolute Priority Rule is the Chapter 11 principle reflected in Bankruptcy Code Section 1129(b) that, in specified cramdown circumstances, prevents a junior class from receiving or retaining property on account of its junior claim or interest when a senior dissenting class is not paid in full.
Accounts Payable
**Accounts payable** are amounts owed to suppliers for goods or services a company has received but has not yet paid for. They are generally current liabilities and can function as a form of short-term operating financing because the company receives value before cash leaves.
Accounts Receivable
**Accounts receivable** are amounts owed by customers for goods or services a company has already provided but has not yet collected in cash. Companies usually report receivables net of allowances for expected credit losses, returns, discounts or other adjustments.
Accrued Expenses
Accrued expenses are costs a company has incurred but has not yet paid in cash. They are generally recorded as liabilities so expense recognition follows the economic period rather than the payment date.
Accumulated Other Comprehensive Income (AOCI)
Accumulated other comprehensive income is the cumulative equity balance of specified gains and losses recognized in other comprehensive income rather than ordinary net income.
Add-On Acquisition
An add-on acquisition is a company purchased by an existing portfolio company—often a platform company—to expand scale, geography, products, customers, capabilities or market share.

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