Duration tells you how sensitive a debt portfolio is to changes in interest rates and when its cash flows are economically received.
Macaulay duration is a weighted-average time measure; modified duration translates duration into approximate price sensitivity.
As a rule of thumb, if modified duration is 5, a 1 percentage-point rise in yield can imply roughly a 5% price decline before allowing for convexity, coupon accrual, credit changes and portfolio actions.
What this Guide Covers
- Why bond prices move opposite to yields
- Macaulay duration explained simply
- Modified duration and approximate NAV sensitivity
- Average maturity vs duration
- YTM vs return
- Credit risk vs interest-rate risk
- How debt-fund categories use duration
- How falling/rising rate cycles affect funds
- Duration calculator examples
- Fund comparison checklist
Why debt funds can lose money even when bonds pay interest
A debt mutual fund is not a fixed deposit. Its NAV reflects the market value of the bonds it owns. When market interest rates rise, older bonds carrying lower coupons generally become less attractive, so their market prices fall.
When market yields fall, existing higher-coupon bonds usually become more valuable.
A bond’s or portfolio’s price change depends heavily on duration. That is why two debt funds with similar credit ratings and YTMs can behave very differently when interest rates change.
Macaulay duration in plain English
Macaulay duration is the weighted average time, usually expressed in years, until an investor receives the present value of a bond’s cash flows.
Earlier coupon payments get their own weight; the final principal payment usually carries a large weight.
For a zero-coupon bond, Macaulay duration is close to its maturity because all cash arrives at the end.
For a coupon-paying bond, duration is generally shorter than maturity because you receive some cash before the final date.
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Modified duration: the number most investors should connect to NAV risk
Modified duration adjusts Macaulay duration for the bond’s yield and gives an approximate measure of price sensitivity.
The practical shortcut is: percentage price change is approximately minus modified duration multiplied by the change in yield.
If a portfolio has modified duration of 4.5 and market yields rise by 0.50 percentage points, the price impact may be roughly -2.25% before considering convexity, daily accrual, spread changes, portfolio trades and other factors.
If yields fall by the same amount, the approximate price effect goes the other way.
| Modified duration | Yield move | Approx. price effect |
| 1 year | +0.50% | about -0.5% |
| 3 years | +0.50% | about -1.5% |
| 5 years | +0.50% | about -2.5% |
| 7 years | +0.50% | about -3.5% |
| 5 years | -0.50% | about +2.5% |
Average maturity is not the same as duration
Average maturity is the weighted-average time until the securities mature.
Duration goes further by considering cash-flow timing and, in modified form, yield sensitivity. A coupon-paying portfolio can therefore have an average maturity that is longer than its Macaulay duration.
When comparing funds, do not use a single number in isolation. Average maturity, Macaulay duration, modified duration and YTM each answer a different question.
What is YTM and why is it not your guaranteed return?
Yield to Maturity (YTM) is the annualised yield implied by a bond’s current price and promised cash flows, assuming it is held to maturity and the calculation assumptions hold.
A portfolio YTM is therefore a useful snapshot of the yield environment and credit/spread compensation.
But a mutual fund does not promise that YTM to you. Returns can differ because of expenses, defaults/downgrades, cash flows, portfolio turnover, reinvestment, interest-rate moves and your own entry/exit date.
A high YTM can also be compensation for higher credit risk.
Interest-rate risk vs credit risk
Interest-rate risk is the risk that bond prices change because market yields change. Credit risk is the risk that an issuer’s ability or willingness to pay deteriorates.
Duration mostly helps you understand the first risk; ratings, spreads, issuer concentration and balance-sheet quality help you understand the second.
A fund can have low duration but still take substantial credit risk. Conversely, a gilt fund can have minimal corporate default risk but very high duration and therefore large NAV swings when yields move.
How SEBI debt-fund categories use duration
India’s debt-fund categorisation includes schemes positioned across very short, short, medium and long duration ranges, along with categories defined by issuer/credit strategy.
SEBI issued a new categorisation and rationalisation circular in February 2026, so investors should check the latest category definitions in the current SID/factsheet rather than rely on an old chart from previous years.
The broader principle remains intuitive: funds designed around shorter portfolio duration usually have lower sensitivity to rate changes; funds with longer duration generally have more potential upside when yields fall and more downside when yields rise.
How rate cycles affect debt funds
When investors expect rates to decline, long-duration portfolios can benefit because existing bonds may appreciate as yields fall.
When rates rise unexpectedly, the same portfolios can take mark-to-market losses.
Short-duration funds experience smaller price swings, but that does not mean they are risk-free. Credit events, liquidity stress and reinvestment at lower yields can still affect outcomes.
How to compare two debt mutual funds
- Start with category and investment mandate
- Compare Macaulay/modified duration
- Compare YTM but investigate why one is higher
- Check rating distribution and issuer concentration
- Review average maturity
- Check portfolio liquidity
- Compare expense ratio
- Review Riskometer
- Check any segregated portfolio history
- Match expected holding period to the fund’s risk profile
Example: choosing between a 1.5-year and 6-year duration fund
If you need your money in nine months, a 6-year duration fund creates a large interest-rate mismatch, even if its recent return looks attractive.
A short-duration strategy may align better with the liability date, though credit and liquidity still need review.
If the horizon is several years and the investor deliberately wants to take duration exposure, the longer fund can be appropriate within a diversified allocation.
The correct question is not “which duration earns more?” but “which interest-rate sensitivity fits this goal and risk capacity?”
Frequently Asked Questions
Is higher Macaulay duration good or bad?
Neither by itself. Higher duration means greater interest-rate sensitivity, which can help when yields fall and hurt when yields rise.
What is the difference between Macaulay and modified duration?
Macaulay duration is a weighted-average timing measure; modified duration converts it into an approximation of price sensitivity to yield changes.
Can modified duration predict exact NAV change?
No. It is an approximation. Convexity, spread changes, accrual, credit events and portfolio trades matter.
Does high YTM mean high return?
No. YTM is a portfolio yield indicator, not a guaranteed return for investors.
Can a gilt fund lose money?
Yes. Government securities largely remove corporate default risk, but long-duration gilt funds can be volatile when interest rates move.
Disclaimer: This article is for education and general information. It is not investment, legal or tax advice. Readers should verify current rules and, where appropriate, consult the relevant intermediary, company, registrar, tax professional or legal adviser.