A bond's yield describes a relationship between price and cash flows. Duration helps answer a different question: how sensitive is that price to a change in yield? Ignoring the second question can make an income comparison misleading, especially when two funds offer similar yields but take very different interest-rate exposure.

Duration is useful precisely because it turns a vague concern about rates into an approximate scenario. It does not predict the next market move, guarantee a recovery period, or summarize every risk in a bond. This guide uses hypothetical examples to show what the number means, where the approximation helps, and where a more detailed analysis is needed.

Distinguish maturity from sensitivity

Maturity is the date when a bond's principal is scheduled to be repaid. Duration is related to the timing and value of its cash flows, but it is not simply another name for that date. Two bonds maturing on the same day can have different sensitivity if their coupons or other features differ.

The type of duration also matters. Macaulay duration describes a present-value-weighted time to cash flows. Modified duration translates that relationship into a local price sensitivity under a specified yield convention. Effective duration is commonly used when modeled cash flows can change as rates change, such as for securities with embedded options.

When reading a fund page, retain the full label instead of copying a bare number. A comparison that mixes effective duration for one portfolio and another duration measure for a different portfolio needs a methodological explanation. Our bond yield guide keeps these terms distinct from yield to maturity.

Use the first-order rule carefully

A common approximation is: percentage price change is roughly negative duration multiplied by the change in yield, with the yield change expressed as a decimal. If modified duration is five and yield rises by one percentage point, the estimated price change is approximately negative 5%.

If yield instead falls by half a percentage point, the same first-order estimate is positive 2.5%. This is a local sensitivity calculation, not a forecast that a particular rate move will occur. It also omits convexity and any other changes in the security or market environment.

Keep percentage points and percentage changes separate. A yield moving from 4% to 5% rises by one percentage point, or one hundred basis points. Feeding “1” into a formula expecting “0.01” would inflate the modeled price movement by a factor of one hundred.

Translate the approximation into dollars

Consider a fictional $10,000 bond position with duration two and another $10,000 position with duration seven. For the same one-percentage-point increase in yield, their first-order price changes would be about negative $200 and negative $700 respectively, before income and other effects.

Now suppose their quoted annual yields differed by only 0.30 percentage points. On $10,000, that headline difference corresponds to roughly $30 over a year under a simplified comparison. The point is not that the longer-duration position is necessarily inappropriate. It is that a small income difference can come with a much larger difference in price sensitivity.

Putting both figures in dollars makes the tradeoff visible. A table containing only the yield percentages would hide it. The bond comparison worksheet places duration beside the yield convention, intended holding period, and possible sale date for exactly this reason.

Include income without claiming certainty

A rate increase can lower a bond's current market price while the investor continues receiving scheduled coupons. A short-horizon scenario should therefore show both components: price change and income received. Looking at only one can exaggerate either the attraction or the damage.

For a simplified one-year illustration, assume 4% income and an immediate 5% price decline, with no other changes. Adding those components suggests approximately negative 1% before fees, taxes, timing effects, and reinvestment. It is deliberately rough, not a complete bond-pricing model or a promised holding-period return.

A real outcome depends on when yields move, how cash flows evolve, what gets reinvested, and whether a sale occurs. The bond yield article explains why a quoted YTM and realized return should not be treated as synonyms. Duration helps build a scenario; it does not finish the entire forecast.

Understand the limits of a straight-line estimate

Bond prices generally do not move along a perfectly straight line as yields change. Convexity describes the curvature that a first-order duration estimate leaves out. For larger yield changes, that omitted curvature can become more important, and the simple approximation can become less accurate.

Embedded options add another complication because cash-flow timing can change. A callable security may be redeemed when doing so benefits the issuer. Mortgage-related cash flows can respond to borrower behavior. Effective-duration models attempt to account for such changes, but their answers depend on assumptions about the future.

You do not need to build an advanced model to recognize its limitations. Label the duration calculation as approximate, keep the assumed yield movement visible, and avoid expressing the result to an implausible number of decimal places. Precision in presentation should not exceed precision in the underlying model.

A fund is not the same as a single maturing bond

An individual nondefaulting bond held to maturity has a specific contractual repayment schedule. A conventional open-ended bond fund continually holds and trades a portfolio, so the investor should not assume the fund's share price will return to a chosen purchase price on a specific date.

A fund's duration is a portfolio characteristic at an observation date. It can change as holdings, cash flows, market conditions, and portfolio decisions change. A fact sheet from several years ago is therefore not enough to describe the current sensitivity of a position.

Defined-maturity funds have a different structure again, with their own documents and end-of-life mechanics. The lesson is to identify the investment vehicle rather than transferring a single-bond intuition to every product with the word “bond” in its name. Our ETF guide connects this issue with fund income measures.

Interest rates are only one source of loss

A corporate bond's yield can change because the market's required compensation for credit risk changes, not just because government benchmark rates move. Liquidity, issuer events, and other factors can also affect the price available to a seller. A duration number does not explain all those mechanisms by itself.

For a simple stress record, separate a broad rate move from a credit-spread change and an adverse liquidity event. Avoid assuming each has a known probability merely because it can be listed. The purpose of an initial worksheet is to identify what the money is exposed to, not to produce an unsupported expected-loss score.

Short duration does not automatically mean low overall risk. A short-maturity issuer with serious repayment problems can still produce a severe loss. Conversely, high credit quality does not eliminate sensitivity to rates. Keeping the dimensions separate is more useful than calling a product simply “safe” or “risky.”

The takeaway: put duration next to the yield

Duration gives an approximate language for interest-rate sensitivity. Read the precise measure, match the observation dates, convert plausible yield moves into dollar scenarios, and keep income separate from price change. Then consider the investment's intended holding period and the other risks the duration calculation leaves out.

Do not use the result as a prediction of a rate move or as a guarantee of when losses will be recovered. For the underlying relationship between duration, changing rates, and bond prices, see FINRA's guide to interest-rate changes and duration. The comparison framework applies the same discipline to other yield categories.