Bond Duration and Interest-Rate Risk: How Rising Yields Affect Bond Prices
Bond duration tells you how much a bond’s price will change when interest rates move. When yields rise, bond prices fall, and the longer the duration, the bigger the fall. A bond with a modified duration of 7 loses about 7% of its price for every 1 percentage point rise in yield.
Most Indian investors think of bonds and debt funds as the safe side of a portfolio. That is mostly true for default risk, but it says nothing about interest rate risk. If you have ever seen a gilt fund or a long duration fund show a negative return in a year when the fixed deposit rate was 7%, you have met this risk firsthand. This guide explains what bond duration is, how rising yields affect bond prices, how to calculate duration, and how to use it when you pick bonds or debt mutual funds.
What Is Bond Duration?
Bond duration is a measure of a bond’s sensitivity to changes in interest rates. It is expressed in years, but it is not the same as the time left until maturity. Duration works like a weighted average of the time you wait to receive each cash flow from the bond, including every coupon payment and the final principal repayment.
There are two ways to read the number:
- As a time measure. Duration is the weighted average time, in years, it takes to get your money back through coupons and principal.
- As a price sensitivity measure. Duration estimates the percentage change in a bond’s price for a 1% change in yield.
The second reading is the one investors use most. If a bond has a duration of 5 years, a 1% rise in yields will push its price down by roughly 5%, and a 1% fall in yields will push its price up by roughly 5%.
Why Bond Prices Fall When Yields Rise
The bond price and yield relationship is inverse. This surprises many first-time investors, but the logic is simple.
Suppose you buy a bond that pays a fixed coupon of 7% on a face value of ₹1,000. A year later, the market changes and new bonds of similar quality pay 8%. Nobody will pay ₹1,000 for your 7% bond when ₹1,000 buys a new bond paying 8%. To sell yours, you must cut the price until the buyer’s overall return, which is the yield to maturity, matches what the market now offers.
So the price falls. The coupon on your bond has not changed at all. What changed is the rate investors demand, and the price moves to adjust for it.
The reverse also holds. If market yields drop to 6%, your 7% bond becomes more valuable, and its price rises above face value.
Types of Duration: Macaulay, Modified and Effective
You will see three kinds of duration in bond literature.
Macaulay duration is the weighted average time to receive all cash flows, measured in years. It is named after Frederick Macaulay, who introduced the idea in 1938. A zero coupon bond has a Macaulay duration equal to its maturity, because you receive everything at the end.
Modified duration adjusts Macaulay duration for the yield level. It is the number that directly tells you the price change for a 1% change in yield. The formula is:
Modified Duration = Macaulay Duration / (1 + yield per period)
Effective duration is used for bonds with embedded options, such as callable bonds, where cash flows can change when rates change. It is calculated by repricing the bond at slightly higher and lower yields and measuring how the price responds.
For a plain government security or a standard corporate bond, modified duration is the one to focus on.
How to Calculate Bond Duration: A Worked Example
Take a 10-year bond with a 7% annual coupon, a face value of ₹1,000, and a yield to maturity of 7%. The bond trades at par.
Using the standard formula for Macaulay duration, this bond works out to about 7.52 years. Dividing by 1.07 gives a modified duration of about 7.02.
Now test it. If the yield rises from 7% to 8%, the price becomes about ₹932.90, a fall of 6.71%. The duration estimate said about 7.02%, so it is close, though not exact. We will come back to why in the convexity section.
Compare this with a 3-year bond that has the same 7% coupon and 7% yield. Its Macaulay duration is about 2.81 years and its modified duration is about 2.62. If yields rise by 1%, its price falls to about ₹974.23, a drop of only 2.58%.
| Feature | 10-year, 7% coupon bond | 3-year, 7% coupon bond |
|---|---|---|
| Macaulay duration | About 7.52 years | About 2.81 years |
| Modified duration | About 7.02 | About 2.62 |
| Price if yield rises 1% | About ₹932.90 (down 6.71%) | About ₹974.23 (down 2.58%) |
| Price if yield falls 1% | About ₹1,073.60 (up 7.36%) | About ₹1,026 (up about 2.7%) |
Same coupon, same starting yield, very different outcomes. The longer bond carries far more interest rate risk.
What Makes Duration Higher or Lower?
Three factors decide a bond’s duration.
Maturity. A longer maturity means a longer duration. The principal is paid further away, so its present value is hit harder when yields rise.
Coupon rate. A higher coupon means a lower duration. A bigger share of your return arrives early through coupons, so the weighted average wait is shorter. Zero coupon bonds have the highest duration for a given maturity.
Yield level. A higher yield means a slightly lower duration. When yields are high, distant cash flows are discounted more heavily and matter less in the weighted average.
This is why a 30-year zero coupon bond is among the most rate-sensitive instruments in fixed income, while a 91-day treasury bill barely moves.
Bond Convexity: Why Duration Is Only an Estimate
Look back at the 10-year bond example. A 1% rise in yield cut the price by 6.71%, but a 1% fall raised it by 7.36%. Duration alone would predict 7.02% in both directions.
The gap exists because the price and yield relationship is a curve, not a straight line. The measure of that curvature is called bond convexity. Positive convexity works in the investor’s favour: for the same size of yield move, the price gain when yields fall is larger than the price loss when yields rise.
For small yield changes, duration is accurate enough. For large moves of 1% or more, convexity matters, and ignoring it understates the gains and overstates the losses on a plain bond.
What Rising Yields Look Like in India Right Now
This is not a textbook issue. Indian bond investors are living through it.
India’s 10-year government security started 2026 at around 6.6%. The benchmark 10-year yield was hovering near 6.6% in early January 2026. By mid-October, the yield had risen to 7.38%, its highest level in more than three years, after the RBI tightened liquidity and shifted to a hawkish stance. The RBI had raised its repo rate by 25 basis points to 5.50%, its first hike since February 2023. Economists now expect the repo rate to reach at least 6% before this cycle ends.
Let us put that in numbers. The 10-year yield moved up by roughly 75 to 77 basis points over about nine months. A bond with a modified duration near 7 would have lost roughly 5% of its price from that move alone, before counting coupon income. That is why long duration debt funds have had a rough year, even though no borrower defaulted.
Short duration funds and floating rate instruments have held up far better, because their prices barely react to yield changes.
Bond Duration in Debt Mutual Funds
Most retail investors in India meet duration through debt mutual funds, not individual bonds. For a fund, duration is the weighted average of the durations of every bond it holds. It appears in the fund factsheet as Macaulay duration or modified duration.
SEBI sorts debt fund categories largely by Macaulay duration:
| Category | Macaulay duration |
|---|---|
| Overnight fund | 1 day |
| Liquid fund | Up to 91 days |
| Ultra short duration fund | 3 to 6 months |
| Low duration fund | 6 to 12 months |
| Short duration fund | 1 to 3 years |
| Medium duration fund | 3 to 4 years |
| Medium to long duration fund | 4 to 7 years |
| Long duration fund | More than 7 years |
| Gilt fund with 10-year constant duration | About 10 years |
SEBI also publishes a Potential Risk Class matrix for debt funds. The interest rate risk axis has three classes. Class I covers a Macaulay duration of up to 1 year, Class II covers up to 3 years, and Class III covers any duration. A fund labelled Class III on interest rate risk can swing sharply when yields move.
On taxation, debt fund units bought on or after 1 April 2023 are generally taxed at your income tax slab rate, regardless of holding period. Check the current rules or speak to a tax adviser before you decide, since the details have been revised more than once.
How to Manage Interest Rate Risk in a Bond Portfolio
You cannot control where yields go. You can control how much of that movement you are exposed to.
Match duration to your holding period. If you need the money in three years, a fund with a duration near three years is a sensible fit. Gains and losses from yield changes tend to balance out around the duration date, so a matched horizon reduces the effect of rate swings on your final outcome.
Shorten duration when yields look set to rise. In a rising rate cycle like the current one, short duration, low duration and floating rate options carry less price risk. The trade-off is that you give up the price gains if yields later fall.
Build a bond ladder. Spread money across bonds maturing in different years, such as 1, 3, 5 and 7 years. As each bond matures, reinvest at the then-current yield. A ladder smooths out the effect of any single rate move.
Consider a barbell or bullet structure. A barbell holds short and long bonds with nothing in the middle. A bullet concentrates holdings around one maturity. Each shapes your duration and your reaction to changes in the yield curve differently.
Use target maturity funds for a fixed horizon. These funds hold bonds that mature near the fund’s end date, so the duration shrinks as time passes. If you hold to the target date, the yield at purchase is a reasonable guide to what you will earn, subject to credit quality.
Hold to maturity for individual bonds. If you buy a bond and keep it until it matures, you receive the full principal and coupons regardless of interim price swings. The mark-to-market loss is real on paper but does not become a cash loss unless you sell.
Interest Rate Risk and Reinvestment Risk Work in Opposite Directions
Rising yields hurt existing bond prices, but they also mean new money and maturing coupons can be reinvested at higher rates. This is called reinvestment risk when yields fall and reinvestment benefit when yields rise.
For a long term investor, this partly offsets the price loss. The point at which the two effects cancel out is, in simple terms, the duration of the bond. This is one more reason duration matters: it tells you how long you need to hold for the higher reinvestment income to make up for the price drop.
Common Mistakes Investors Make With Bond Duration
- Treating all debt funds as safe. Low credit risk does not mean low price risk. A gilt fund has no default risk but can lose money when yields climb.
- Chasing the highest yield. A higher yield often comes with a longer duration or lower credit quality. Look at both.
- Ignoring duration in the factsheet. The Macaulay or modified duration of a fund is published every month. Read it before investing.
- Confusing maturity with duration. A 10-year bond with a high coupon has a duration well below 10 years.
- Expecting duration to be exact. It is a first-order estimate. For big yield moves, convexity changes the result.
- Switching funds after the fall. Selling a long duration fund after yields have already risen locks in the loss and misses the higher yields available going forward.
Frequently Asked Questions
What is bond duration in simple terms?
Bond duration is a measure, in years, of how sensitive a bond’s price is to a change in interest rates. A higher duration means a bigger price swing when yields move.
Why do bond prices fall when interest rates rise?
Existing bonds pay a fixed coupon. When new bonds offer higher rates, buyers pay less for older, lower-paying bonds. The price drops until the older bond’s yield matches the market.
What is the difference between Macaulay duration and modified duration?
Macaulay duration is the weighted average time to receive a bond’s cash flows, in years. Modified duration is Macaulay duration divided by one plus the yield, and it gives the percentage price change for a 1% change in yield.
How do you calculate the price change using duration?
Multiply the modified duration by the change in yield and reverse the sign. For a modified duration of 6 and a 0.5% rise in yield, the estimated price change is about minus 3%.
Which bonds have the highest interest rate risk?
Long maturity bonds with low coupons, and zero coupon bonds, have the highest duration and the most price risk when yields rise.
What is a good duration for a bond fund?
It depends on your holding period and view on rates. A common rule is to choose a fund whose duration is close to the time you plan to stay invested.
Do rising yields affect gilt funds?
Yes. Gilt funds hold government securities with no default risk, but their prices are sensitive to yield changes, especially long duration and constant maturity gilt funds.
Is it a good time to invest in debt funds when yields are rising?
Rising yields lower prices of existing bonds but raise the income on new investments. Shorter duration funds usually suit a rising rate phase better, while longer duration funds tend to benefit when yields fall. This is general information and not personal advice.
What is the relationship between the RBI repo rate and bond prices?
When the RBI raises the repo rate, market yields generally move up, and bond prices fall. When it cuts the repo rate, yields generally fall and bond prices rise. Bond markets often move before the RBI acts, based on what traders expect.
Can I lose money in a government bond?
You will not lose principal from default if you hold to maturity. You can lose money on paper, or in reality if you sell early or hold a bond fund, when yields rise and prices fall.
Final Thoughts
Bond duration turns a vague worry about interest rates into a number you can use. Before buying any bond or debt fund, find its duration, ask what a 1% rise in yields would do to the price, and check that the answer fits your holding period and your comfort level.
In a period of rising yields, as India is seeing now, that single check can save you from a loss you did not expect. Short duration protects you while rates climb. Longer duration rewards patience when they eventually fall. Choose based on when you need the money, not on last year’s returns.
Disclaimer: This article is for educational purposes and is not investment advice. Bond prices, yields and tax rules change. Please check current data and consult a SEBI-registered investment adviser before making decisions.