Fund Duration vs Individual Bond

An individual bond has a maturity date when you get your principal back. A bond fund has no such date. Instead, it manages a rolling portfolio where bonds mature, are sold, and are constantly replaced. Duration, not maturity, describes how sensitive the fund is to interest rate moves.

Key takeaways

• Individual bonds mature at a stated date; bond funds continuously replace maturing bonds with new ones
• Duration measures interest rate sensitivity in both cases, but the analogy breaks down when rates change
• A 5-year duration fund isn't equivalent to a 5-year bond; the fund reprices continuously
• Rolling portfolio mechanics mean bond funds can hold steady duration while replacing every bond
• Understanding this difference prevents the "maturity misconception"—the idea that funds eventually return principal to par

The individual bond maturity principle

When you buy an individual bond—say, a 10-year Treasury issued on January 1, 2024—you have a contract:

• The issuer pays you a fixed coupon (e.g., 4%) semi-annually
• On January 1, 2034, the issuer redeems your bond for $1,000 (par)
• Until that date, the bond's price fluctuates with interest rates, but you can hold to maturity and collect par
• The maturity date is fixed and final

If you buy at $1,000, rates don't matter for final principal recovery. You get $1,000 back, no matter if rates rose to 6% or fell to 2%. The bond's duration—how long it takes for reinvested coupons and principal to return to you—is roughly 8 years (less than the 10-year stated maturity, because coupons arrive earlier).

Maturity is a hard boundary. You know the endpoint.

How bond funds replace bonds instead

A bond fund doesn't hold individual bonds until maturity. Instead, it:

1. Receives principal from maturing bonds — holdings constantly reach their maturity dates
2. Sells bonds before maturity — to rebalance, capture gains, reduce risk, or raise cash for redemptions
3. Buys new bonds — to replace the sold or matured ones
4. Manages overall duration — keeps the fund's rate sensitivity in a target band (e.g., 4–6 years)

Consider the BND (Vanguard Total Bond Market ETF). On any given day, BND holds thousands of bonds across Treasury, corporate, and mortgage sectors. Some mature within weeks. Some don't mature for 30 years. But the fund's weighted average maturity is roughly 6 years.

As bonds mature, the fund receives cash and instantly faces a choice: buy new bonds to replace them. If the fund replaces a matured 6-year Treasury with a new 6-year Treasury, the fund's overall duration stays the same. The maturity date of each individual holding changes, but the fund's profile doesn't.

If new 6-year yields are lower than the old bond's coupon, the fund's distribution will fall. That's a real change. But the fund didn't "mature"—it just rolled over.

Duration: the shared measure

Both individual bonds and bond funds use duration to describe interest rate sensitivity. Duration answers: "If yields rise by 1%, how much will this bond or fund fall in price?"

A bond with 5-year duration falls about 5% if yields jump from 4% to 5%. A bond fund with 5-year duration also falls about 5% in the same scenario. In this sense, they're comparable.

But the comparison is shallow. Here's why:

Individual bond: Duration tells you how long until you get principal back (weighted by the timing of coupons). After 10 years, when the bond matures, its duration is zero—your principal is returned. Duration is a measure of time and cash flow.

Bond fund: Duration is a mathematical sensitivity measure. It doesn't predict when principal is returned because there is no return date. The fund's duration is maintained by continuously rolling the portfolio.

What happens when interest rates rise sharply

Imagine rates rise from 4% to 6% immediately.

Your 10-year individual bond:

• Loses market value (price falls)
• Duration shrinks because you're now closer to maturity—the 10-year still matures in 10 years, but the relative value of the near-term coupon grows
• You can either hold to maturity (recover par in 10 years) or sell at a loss
• If held to maturity, you get $1,000 back, but you've locked in 4% returns on an old coupon while new bonds pay 6%

A bond fund with 5-year duration:

• Falls by roughly 5% in price
• Duration also shrinks slightly as yields rise (this is "convexity")
• But the fund doesn't have a "recovery date" like the bond
• The fund will replace maturing or sold bonds with new 6% bonds, lowering its distribution yield
• If you hold the fund for 10 years, you don't get par back; you get whatever NAV is at that time

The key insight: the individual bond has a redemption date that guarantees par recovery (assuming no default). The fund has no such date. If rates stay high, your fund's NAV stays depressed indefinitely—you don't eventually recover the principal loss by holding to maturity, because there is no maturity date.

The rolling portfolio in action

Here's a simplified example of how a bond fund maintains duration:

Year 1:

• Fund holds 100 bonds, mostly with 4–7 years to maturity
• Weighted average duration: 5 years
• Weighted average maturity: 5.5 years

Year 2:

• Some bonds have matured or been sold
• Interest rates remain unchanged
• The remaining bonds are now closer to maturity (the 5-year bonds are now 4-year bonds)
• The fund's duration would naturally shrink
• To maintain the 5-year target, the fund buys longer-dated bonds (7–10 year) to replace sold or matured ones

Result: The fund's duration stays at 5 years, but the specific bonds in it have changed. You've sold old bonds and bought new ones. If the new bonds offer lower yields (normal in an unchanged-rate environment), your distribution will decline slightly.

Duration alone isn't enough for comparison

Knowing a fund has 5-year duration doesn't tell you what returns to expect. You also need:

• Yield — what's the current SEC or distribution yield?
• Credit quality — are bonds Treasuries, corporates, or mixed?
• Convexity — how much does duration change as yields move? (Mortgage funds have negative convexity; they lose duration gains when rates fall because homeowners refinance.)
• Reinvestment risk — when coupons arrive, what rate can you earn reinvesting them?

Two funds with identical 5-year duration can deliver very different returns if one holds 100% Treasuries at 4% yield and the other holds corporate bonds at 5% yield.

When do you get your principal back from a fund?

You never do—not in the way an individual bond works. You get principal only when you sell your fund shares. At that time, you might get more than you invested (if NAV rose), less than you invested (if NAV fell), or exactly what you invested (if NAV is unchanged).

If you bought $10,000 of BND and rates rose, NAV fell to $9,800. You can sell for $9,800, taking a loss, or hold. But there's no maturity date on which the fund will pay you $10,000. The fund holds thousands of individual bonds with thousands of maturity dates, but the fund itself has no maturity.

For long-term investors who buy and hold, this is not a problem. Over decades, rising coupons and principal repayments from maturing bonds provide cash flow. But it means bond funds are not substitutes for individual bonds if you're trying to guarantee a principal return at a specific date.

Practical implications for your portfolio

If you need principal in 5 years and want zero interest rate risk, buy a 5-year individual bond, not a 5-year duration bond fund. The individual bond's maturity date guarantees you par (or you can reinvest maturing bonds into new 5-year bonds to extend).

If you're building a portfolio for 20+ years and want flexibility, a bond fund with appropriate duration is ideal. You don't have to ladder individual bonds; the fund does the reinvestment for you.

If you're unsure when you'll need the cash, a short-duration fund (1–3 years) limits your downside if rates spike, but it also means lower yield and more reinvestment rate risk as bonds mature quickly.

The maturity-vs-duration distinction matters most when interest rates change sharply and you have a specific future date for needing cash.

Next

The mechanics of rolling portfolios and duration management reveal why bond funds respond differently to rising rates than you might expect. A fund with 5-year duration will fall in value when rates rise, but that fall is permanent—the fund doesn't "mature back to par" the way an individual bond does if held to maturity. Understanding this sets up the next topic: what happens to bond funds when the Federal Reserve raises rates, and why the 2022 bond bear market was so severe for fund holders.

Related concepts

• Bond Fund Mechanics
• Aggregate Bond Funds (BND, AGG)