Direct answer: Bond duration measures a bond's sensitivity to interest rate changes. Modified duration expresses the approximate percentage change in a bond's price for a 1% (100 basis point) change in yield. A bond with a modified duration of 7 will lose approximately 7% of its value if interest rates rise by 1%. Duration increases with maturity and decreases with coupon rate: a 30-year zero-coupon bond has much higher duration (and therefore much more interest rate risk) than a 2-year note.
Fact Sheet: Bond Duration and Interest Rate Risk
Key Takeaways
- Macaulay duration is the weighted average time to receive a bond's cash flows (coupon payments and principal), measured in years. Modified duration = Macaulay duration divided by (1 + yield per period) and is the practical measure used for price sensitivity calculations.
- A bond fund's effective duration is the weighted average of the individual bond durations in the portfolio; Vanguard Total Bond Market ETF (BND) had an effective duration of approximately 6 years in 2021, which contributed to its approximately 13% loss when rates rose sharply in 2022.
- The price change approximation: price change percentage equals negative modified duration times change in yield. For a duration-7 bond: a 2% yield increase produces approximately -14% price change; a 2% yield decrease produces approximately +14% price change. This approximation is linear; the actual price change is convex (slightly better than the linear approximation for large rate moves).
- Duration and maturity are related but not identical: a 10-year 5% coupon bond has lower duration than a 10-year zero-coupon bond because coupon payments return cash sooner, reducing the weighted average time to receive cash flows.
- Investors who need a specific amount of money at a specific future date can match that date's duration using bonds or bond funds (immunization), protecting against interest rate risk for that specific cash flow need.
Duration Calculation Example
A simple 3-year bond paying a 5% annual coupon on $1,000 face value: Year 1 cash flow $50 (weight = 50/1,150 = 4.3%), Year 2 cash flow $50 (weight = 4.3%), Year 3 cash flow $1,050 (weight = 91.4%). Macaulay duration = (1 year times 4.3%) + (2 years times 4.3%) + (3 years times 91.4%) = 2.83 years. At a 5% yield, modified duration = 2.83 / (1 + 0.05) = 2.70. For a 1% rate increase, the bond loses approximately 2.70% in value. For a 30-year zero-coupon bond, Macaulay duration equals maturity (30 years) and modified duration at 5% yield equals 28.6, making it nearly 10 times more rate-sensitive than the 3-year bond.
The 2022 Bond Market Case Study
The U.S. Federal Reserve raised the federal funds rate from near 0% in January 2022 to 4.25% to 4.5% by December 2022, a 4.25 percentage point increase over 12 months. For the Vanguard Total Bond Market ETF (BND), which had an effective duration of approximately 6.6 years at the start of 2022: price change approximation = -6.6 times 4.25% = -28% price decline. BND's actual total return for 2022 was approximately -13% (the yield income of about 2% per year partially offset the price decline, and the convexity of bond prices was positive). This was the worst year for U.S. investment-grade bonds since at least 1976. Investors who held bonds for their 'safe' characteristics experienced larger losses than in many equity bear markets.
Duration Management Strategies
Short duration for rising rate environments: short-term bond funds (duration 1 to 3 years) lose much less than intermediate or long-term funds when rates rise; at the cost of lower yield in normal environments. Laddering: holding bonds maturing in 1, 2, 3... years distributes reinvestment risk across the yield curve; as short bonds mature, proceeds are reinvested at current rates. TIPS (Treasury Inflation-Protected Securities): their duration is to real rates, not nominal; they provide inflation protection but have nominal duration similar to comparable maturity nominal Treasuries. Floating rate bonds: coupon resets periodically with market rates, so price sensitivity is very low (short effective duration) despite long nominal maturity.
Duration in Bond Fund Selection
Every bond fund reports its effective duration; comparing funds requires looking at this metric, not just maturity. A corporate bond fund and a government bond fund with the same maturity profile will have similar durations if the coupon rates are similar; the differences come from credit risk rather than duration. Typical durations: ultra-short bond funds (1 year or less), short-term bond funds (2 to 3 years), intermediate-term (4 to 6 years), long-term (10 to 20 years), extended maturity (20+ years). Total bond market funds typically have intermediate durations (5 to 7 years). Investors seeking to reduce interest rate risk should check a fund's effective duration, not just its name or maturity label.
Frequently Asked Questions
Does duration tell me everything I need to know about bond risk?
No. Duration captures interest rate risk (sensitivity to parallel shifts in the yield curve) but not credit risk (probability of default or downgrade), liquidity risk (ease of selling without price impact), inflation risk (loss of purchasing power), call risk (for callable bonds, the issuer can repay early when rates fall, limiting upside), or prepayment risk (for mortgage-backed securities). A comprehensive bond risk assessment uses duration alongside credit rating, spread to treasuries, and liquidity metrics.
Why did bonds lose money in 2022 if they are considered safe?
Bonds carry interest rate risk (price falls when rates rise) and credit risk. 'Safe' typically refers to credit quality (low probability of default for investment-grade and government bonds), not absence of price volatility. A long-duration government bond has no credit risk but substantial interest rate risk. The 2022 decline was almost entirely from the rate increase, not from credit deterioration. Short-term government bonds (T-bills, I-bonds) were relatively unaffected by the 2022 rate increases because their short duration meant minimal price sensitivity. The distinction between 'safe from default' and 'safe from price decline' is important when evaluating bonds as portfolio stabilizers.
How should I think about bond duration relative to my investment horizon?
A general principle: match your investment horizon to the duration of your bond holdings. If you plan to hold for 3 years and then spend the proceeds, a bond fund with 5 to 6 year duration exposes you to more price risk than a fund matching your horizon. If rates rise sharply over the 3 years, you may be selling at a loss even though you would have 'recovered' if you held longer. Investors with long horizons (10+ years) can tolerate more duration because they capture the higher yields that come with longer maturity bonds and are less exposed to having to sell at a low point.