3 key metrics to evaluate before investing in debt funds: Average maturity, macaulay duration, and modified duration
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- Debt funds invest in fixed-income securities such as government securities, treasury bills, corporate bonds, debentures, and commercial papers, with returns dependent on the performance of underlying debt securities and movements in interest rates.
- Average maturity represents the weighted average time remaining for all debt securities in a fund's portfolio to mature, with higher average maturity indicating greater sensitivity to interest rate changes.
- Macaulay duration estimates the average time required to recover a fund's investment through coupon payments and principal repayment, with higher values indicating greater interest rate risk.
- Modified duration estimates the percentage change in a bond's price for a 1% change in interest rates—a modified duration of 5 means a fund's NAV can be expected to rise or fall by approximately 5% for every 1% move in rates.
- In a hypothetical comparison of two medium-duration funds, Fund B's Macaulay duration of 6 years and modified duration of 5.5 would mean a 1% rate rise could cause an approximate 5.5% NAV decline, versus 2.3% for Fund A (Macaulay duration 2.5 years).
- The article concludes there is no single best debt fund—the right choice depends on the investor's interest rate outlook and risk appetite, with lower-duration funds better suited for expected rate hikes and higher-duration funds positioned to benefit from rate declines.
Why it matters: Choosing a debt fund based purely on past returns—rather than interest rate sensitivity metrics—can leave investors exposed to sharper NAV declines when rates shift. The article's side-by-side Fund A versus Fund B example shows a 1% rate rise translating to roughly a 5.5% versus 2.3% NAV drop, making the concrete cost of ignoring these metrics visible to retail investors weighing debt fund options.
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