iShares Core U.S. Aggregate Bond ETF (AGG)

What the fund owns and how it works

AGG seeks to track the Bloomberg U.S. Aggregate Bond Index. The benchmark brings together several parts of the taxable, U.S. dollar, investment-grade bond market, including Treasury securities, government-related debt, corporate bonds, agency mortgage-backed securities, commercial mortgage-backed securities, and asset-backed securities. The fund uses the portfolio techniques allowed by its prospectus to approximate that benchmark after expenses and normal implementation effects.

The word aggregate describes a defined index universe, not every bond available to an investor. Maturity, size, currency, credit-quality, and security-type rules determine eligibility. Most municipal debt, below-investment-grade corporate bonds, inflation-linked Treasuries, and many floating-rate or privately placed securities sit outside this benchmark. Mortgage exposure also introduces cash flows that can change as homeowners refinance or repay loans.

Why readers compare or use it

AGG is often examined as a single-fund view of the core investment-grade bond market. Its mix of government, mortgage, and corporate sectors gives it more varied return drivers than a Treasury-only portfolio. Income, changes in Treasury yields, credit spreads, and mortgage prepayment expectations can all affect results.

Readers commonly compare AGG with BND because both occupy the broad core-bond category. That category label can hide meaningful index differences. AGG follows the standard Bloomberg aggregate benchmark, while BND follows a float-adjusted version. The distinction changes how publicly unavailable government holdings are treated and can affect weights and portfolio implementation.

Trade-offs to understand

Broad sector coverage does not remove interest-rate risk. A useful first approximation multiplies a fund's duration by a change in yield to estimate the opposite-direction percentage price move. That relationship is not exact because yields do not move uniformly, cash flows change, and bond prices have curvature. Duration should therefore be shown with a date and used as an explanatory measure, not a forecast.

Credit spreads can widen even when Treasury rates are stable. Mortgage-backed bonds add prepayment and extension risk, while corporate bonds add issuer credit risk. ETF shares also trade at market prices, which may be above or below net asset value. The stated expense ratio does not capture spreads, brokerage terms, taxes, or tracking difference.

Closest alternatives

BND is the nearest broad-market comparison and uses a float-adjusted Bloomberg benchmark. A Treasury fund removes corporate credit and mortgage-prepayment exposure but narrows the opportunity set. LQD concentrates on investment-grade corporate debt, while TIP focuses on inflation-protected Treasuries. HYG moves outside investment grade. These choices change the exposure rather than merely changing the ticker.

What can change

Bloomberg can revise index eligibility, classifications, calculation practices, and rebalancing rules. The portfolio's duration, yield, sector weights, credit mix, holding count, and mortgage characteristics change with markets and index turnover. BlackRock can update fees, sampling practices, service providers, and operating policies through current disclosures. A methodology revision or benchmark change would alter what the fund is designed to hold.

Evidence and links

Primary evidence: the official iShares AGG page, current AGG fact sheet and prospectus, and Bloomberg U.S. Aggregate Bond Index materials.

Editorial sources

• Benchmark source
• Benchmark source
• SEC ETF glossary
• Fund documents
• Fund documents
• Issuer page

Related reading

• BND
• HYG
• LQD
• SCHD
• SGOV
• TIP
• TLT
• USFR
• VIG
• VTV
• Expense ratio
• Inflation
• Liquidity
• Net asset value NAV
• Dividend
• How treasury bills work
• Market index
• What is a bond
• What is an ETF
• What is an index fund
• Yield