Duration is a fixed-income measure of the weighted average timing of a bond’s expected cash flows and, from that timing structure, its first-order sensitivity to changes in yield. In practical terms, it explains why two bonds with the same maturity can still react differently when yields move.
Maturity tells you when principal is due. Duration tells you when a bond’s economic value is effectively returned once coupons and principal are discounted to the present. That is why a ten-year bond can still have a duration well below ten years.
How duration is formed
Duration begins with cash-flow timing. Each coupon payment and the final principal repayment contributes to present value, but they arrive on different dates. Duration measures where the economic center of those discounted payments sits.
Coupon size changes that center. Higher coupons pull duration inward because more value is returned earlier, while lower coupons push duration outward because more value remains in the final payment. A zero-coupon bond shows the logic cleanly: with all value paid at maturity, duration and maturity coincide.
Yield level matters as well. Because duration is built from present values rather than contractual dates alone, a change in yield changes the relative weight of earlier and later cash flows. Duration is therefore a property of the bond at its current price, not a permanent label attached to it.
Remaining time to maturity also changes duration gradually. As coupon dates pass and final repayment comes closer, more of the bond’s value is concentrated in nearer cash flows, so duration usually declines over time unless changes in yield offset that effect.
What duration measures
Bond prices are the present value of future cash flows. When yields rise, those cash flows are discounted more heavily. When yields fall, they are discounted less heavily. Duration summarizes how sensitive price is to that change in discounting.
Shorter-duration bonds usually show smaller price swings because more of their value is recovered sooner. Longer-duration bonds usually show larger price swings because more of their value rests on cash flows that arrive further into the future. In that sense, duration is a bond’s interest-rate sensitivity expressed through cash-flow timing.
Common forms of duration
Macaulay duration refers to the weighted average timing of expected cash flows. Modified duration takes that timing concept and expresses approximate price sensitivity to a small change in yield. In market usage, the word duration is often used broadly, so context determines which meaning is intended.
Macaulay duration answers a timing question, while modified duration answers a price-sensitivity question. They come from the same valuation structure, but they are used differently when describing bond behavior.
Practical distinction: when maturity matters and when duration matters
Use maturity when the question is about contractual length or when principal is due. Use duration when the question is about price sensitivity to changing yields. If the issue is how much a bond may reprice when rates move, duration is usually the more decision-useful measure.
Duration versus maturity
Maturity is a legal endpoint. Duration is a weighted timing measure. The two are related, but they are not interchangeable. Two bonds can share the same maturity and still have different durations if coupon size, yield level, or remaining cash-flow structure differs.
That is why the shortcut “longer maturity means higher sensitivity†is only approximate. Duration is usually the better measure when the question is about interest-rate exposure rather than contract length.
Duration versus duration risk
Duration risk is the exposure created by duration when yields move. Duration itself is the measure: the weighted timing of cash flows and the implied first-order sensitivity of price to yield changes.
The difference is between measurement and exposure. Duration describes the structure of a bond’s cash flows at a given yield level, while duration risk describes the consequence of holding that sensitivity through a rate move.
Duration and discounting
Duration is closely linked to the discount rate, but it is not a discount rate. The rate is the valuation input used to convert future cash flows into present value. Duration measures how strongly bond prices tend to react when that input changes.
Keeping that distinction clear matters because discounting is the mechanism, while duration is the summary measure of exposure to that mechanism.
Where duration fits in equities and bonds analysis
Within Equities and Bonds, duration starts as a bond concept. It explains why different fixed-income instruments respond differently when the yield backdrop changes.
The same discounting logic also sits in the background of why higher yields hurt stocks, especially when valuations depend heavily on cash flows far into the future. Even so, duration remains a bond valuation concept rather than a full explanation of equity performance.
What duration does not capture
Duration does not describe expected return, credit quality, or every source of price movement. Credit stress, liquidity conditions, and issuer-specific events can move bond prices for reasons that sit outside pure rate sensitivity.
It is also a first-order approximation rather than a complete description of every market move. For larger yield changes or more complex instruments, realized price behavior can depart from what duration alone would imply.
FAQ
Does a bond’s duration stay constant over time?
No. As time passes, remaining cash flows shorten and the bond is repriced against current yields. Duration therefore changes with both the passage of time and changes in the yield environment.
Why is modified duration called an approximation?
Because it describes the first-order price response to a small yield change around a given starting point. For larger moves, the price path is not perfectly linear, so duration alone becomes less exact.
Can a long-maturity bond still have relatively low duration?
Yes. A long final maturity does not guarantee extreme sensitivity if substantial coupon payments return value earlier. The cash-flow pattern matters as much as the final repayment date.
Why do zero-coupon bonds make duration easier to understand?
They remove the coupon stream entirely. With all value paid in one final cash flow, the weighted timing measure collapses to the maturity date itself, making the relationship between timing and sensitivity especially clear.