Bond Duration & Interest Rate Risk Explained (Macaulay & Modified Duration)
Two bonds can share the same yield to maturity and still react completely differently when rates move. Duration is the number that tells you which one — with verified worked examples for Macaulay duration, Modified duration, and price sensitivity.
Bond Duration & Interest Rate Risk Explained
Two bonds can have the exact same yield to maturity and still behave completely differently the moment interest rates move. A 2-year Treasury and a 30-year Treasury yielding the same 5% will not lose the same amount of value when rates rise by 1%. Duration is the single number that predicts which bond moves more — and by roughly how much.
- What Macaulay duration actually measures (it is not just "years to maturity")
- Modified duration and how to use it to estimate a price move before it happens
- Why the actual price change never quite matches the duration estimate — and what convexity has to do with it
- Why higher coupons and shorter maturities both mean lower duration
- How to compare interest rate risk across bonds before you buy
What Is Bond Duration?
Macaulay duration is the weighted-average time it takes to receive all of a bond's cash flows, where each cash flow is weighted by its present value. It is measured in years, and it is always less than or equal to the bond's time to maturity — because coupon payments arrive before the final maturity date and pull the average forward.
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| Metric | Value |
|---|---|
| Yield to Maturity | 5.67% |
| Macaulay Duration | 8.05 years |
| Time to Maturity | 10 years |
Modified Duration: Turning Duration Into a Price-Move Estimate
Modified duration converts Macaulay duration into a direct estimate of how much a bond's price will move for a 1-percentage-point change in yield. This is the number that actually matters for risk management.
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| Yield Change | Duration Estimate | Actual Repriced Value | Actual % Change |
|---|---|---|---|
| −2.0% (yield falls to 3%) | +15.44% | $1,170.60 | +17.06% |
| −1.0% (yield falls to 4%) | +7.72% | $1,081.11 | +8.11% |
| +1.0% (yield rises to 6%) | −7.72% | $926.40 | −7.36% |
| +2.0% (yield rises to 7%) | −15.44% | $859.53 | −14.05% |
Duration Estimate vs Actual Price Change
Same 10-year, 5% coupon bond priced at par — the duration estimate is a straight line; the actual price path curves.
- Actual price change
- Duration-only estimate
The gap between the two lines is convexity — and it always works in the bondholder's favor: real gains beat the estimate, real losses fall short of it.
Why the Estimate Is Always a Little Off: Convexity
Modified duration is a straight-line (linear) approximation of a relationship that is actually curved. That curve is called convexity, and it is a small but predictable effect: it makes gains a little bigger than duration predicts when yields fall, and makes losses a little smaller than duration predicts when yields rise. For a 1-percentage-point move, the gap is usually small (in the table above, 0.36 percentage points at ±1%). For a 2-point move, the gap roughly quadruples — which is why duration alone is unreliable for large rate swings, and why professional bond desks add a convexity adjustment on top of it.
What Actually Drives a Bond's Duration
Two variables move duration the most: time to maturity, and coupon rate.
Duration Rises With Maturity (5% Coupon Bond, Priced at Par)
Macaulay duration for the same coupon rate at five different maturities.
2-Year Bond
5-Year Bond
10-Year Bond
20-Year Bond
30-Year Bond
Duration grows more slowly than maturity itself — a 30-year bond has 3x the maturity of a 10-year bond, but only about 2x the duration.
Duration Falls as Coupon Rises (10-Year Bond, Priced at Par)
A higher coupon returns more cash to you earlier, which shortens the weighted-average time to receive your money back.
2% Coupon
5% Coupon
8% Coupon
A zero-coupon 10-year bond would have a duration of exactly 10 years — the maximum possible for that maturity.
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| Factor | Effect on Duration | Why |
|---|---|---|
| Longer time to maturity | Increases duration | More total time before the largest cash flow (face value) arrives |
| Higher coupon rate | Decreases duration | More cash returned early pulls the weighted average forward |
| Lower coupon rate | Increases duration | Less early cash flow — more of the bond's value sits in the final face-value payment |
| Zero-coupon structure | Maximizes duration | All value arrives on a single date — duration equals maturity exactly |
| Higher market yield | Slightly decreases duration | Future cash flows are discounted more heavily, reducing their weight in the average |
Comparing Interest Rate Risk Before You Buy
Short-Duration vs Long-Duration Bonds — Same 1% Rate Move
Modified duration 1.86 years (2-year, 5% coupon bond) versus 15.37 years (30-year, 5% coupon bond), both priced at par.
2-Year Bond (Modified Duration 1.86)
Estimated price move for a 1-percentage-point yield change
- Low interest rate risk
- Price recovers quickly since maturity is near
- Lower long-run yield potential in a normal yield curve
30-Year Bond (Modified Duration 15.37)
Actual repriced move for a 1-percentage-point yield change (rounded from the price table above)
- High interest rate risk
- Locks in today's yield for decades
- Convexity cushions losses and amplifies gains more than a shorter bond
Duration is why a "safe" long-term government bond can still lose double-digit percentage value in a single rate-hiking cycle, while a short-term note barely moves.
Managing Interest Rate Risk in Practice
- Match duration to your time horizon — a bond you plan to hold to maturity carries less practical rate risk than one you might need to sell early.
- Shorten average portfolio duration when you expect rates to rise; lengthen it when you expect rates to fall.
- Diversify across maturities rather than concentrating duration in one bucket — see our guide on bond funds vs individual bonds for how funds handle this automatically.
- Remember duration measures interest rate risk only — it says nothing about credit/default risk. Compare that separately; see Treasury vs Corporate vs Municipal Bonds.
- For a bond you already hold, check its Modified Duration on our Bond Yield Calculator before assuming a rate move will not matter.
What is bond duration in simple terms?
Duration measures how sensitive a bond's price is to changes in interest rates. Macaulay duration expresses this as the weighted-average time to receive all cash flows; Modified duration converts that into a direct price-sensitivity percentage.
What is the difference between Macaulay duration and Modified duration?
Macaulay duration is measured in years — the weighted-average time to cash flows. Modified duration is derived from it (Macaulay ÷ (1 + YTM/frequency)) and estimates the percentage price change for a 1-point yield change.
Is duration the same as maturity?
No. Duration is always less than or equal to maturity for a coupon-paying bond, because coupon payments return some value before the maturity date. Only a zero-coupon bond has duration exactly equal to its maturity.
Why does a higher coupon rate lower duration?
A higher coupon returns more cash to the investor earlier in the bond's life, which pulls the weighted-average time to receive cash flows forward — shortening duration even though maturity is unchanged.
How do I estimate a bond price change from duration?
Use % Change in Price ≈ −Modified Duration × Change in Yield. It is an approximation — accurate for small yield moves, and increasingly imprecise for larger ones due to convexity.
What is convexity and why does it matter?
Convexity is the curvature in the actual price-yield relationship that duration (a straight-line estimate) misses. It benefits bondholders: real price gains from falling yields exceed the duration estimate, and real losses from rising yields fall short of it.
Which bonds have the highest interest rate risk?
Long-maturity, low-coupon bonds have the highest duration and therefore the highest interest rate risk. Zero-coupon long-term bonds carry the most risk of all for a given maturity.
Does duration measure credit risk?
No. Duration measures interest rate risk only — how much a bond's price moves when yields change. It says nothing about the issuer's ability to pay, which is credit risk and must be assessed separately.
How can I lower my portfolio's interest rate risk?
Shorten average duration by holding shorter-maturity or higher-coupon bonds, or diversify across a range of maturities (a bond ladder or a diversified bond fund) rather than concentrating in long-duration bonds.
Where can I calculate a bond's duration?
Our Bond Yield Calculator returns Macaulay and Modified duration alongside YTM and current yield — just enter face value, coupon rate, price, and years to maturity.
Written by
Do The Calculation Team
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Former investment bank strategist and university lecturer with 15+ years of research in compound growth modeling, asset allocation, and annuity projections. Dr. Vance reviews all core investment and retirement tools to ensure absolute alignment with actuarial standards.