Yield Changes of 1 Percent
Yield Changes of 1 Percent
When yields shift by 1 percent, bond prices move by approximately the duration in the opposite direction. This simple relationship—price change ≈ duration × yield change—is the foundation of all practical bond risk management.
Key takeaways
- Duration measures the weighted average time to receive cash flows, expressed in years.
- A bond with 7-year duration loses approximately 7% in value when yields rise 1%.
- This linear approximation works best for small yield changes (under 1–2%).
- Higher-coupon bonds have shorter duration and less price sensitivity.
- Duration is the single most important number for understanding short-term bond portfolio risk.
Understanding Duration
Duration is not maturity. A 10-year bond might have a duration of 8 years if it pays a high coupon; a 5-year zero-coupon bond has a duration of exactly 5 years. Duration captures both when you receive cash and how much you receive, weighted by present value.
Think of it this way: if you own a bond fund, duration tells you how much the fund's value will swing when interest rates move. A fund with 5-year duration will typically lose 5% when yields rise 1%, and gain 5% when yields fall 1%. This is called modified duration in technical terms, and it's what every bond manager uses to size risk.
A Treasury bond maturing in 2035 with a 3% coupon might have a duration around 14 years. That means a 1% yield rise causes a 14% price drop. A short-dated bond fund holding 2–3 year maturities might have duration of 2.5 years, making it much less volatile. The trade-off is clear: lower duration means lower interest rate risk, but also lower yield and lower total return potential over time.
The 1% Rule in Practice
Consider three bonds, all with price 100:
Bond A: 2-year maturity, 2% coupon, duration 1.96 years.
If yields rise 1%, the new price ≈ 100 − (1.96 × 1%) = 98.04.
Bond B: 10-year maturity, 3% coupon, duration 8.5 years.
If yields rise 1%, the new price ≈ 100 − (8.5 × 1%) = 91.50.
Bond C: 30-year maturity, 4% coupon, duration 17.5 years.
If yields rise 1%, the new price ≈ 100 − (17.5 × 1%) = 82.50.
The relationship holds because longer-duration bonds have more cash flows sitting far in the future, so their present value drops more when discount rates rise. A bond paying its full principal in 30 years is hit harder than one paying most of its cash in the next 2 years.
This is why Treasury Inflation-Protected Securities (TIPS), which typically have 5–8 year duration depending on maturity and inflation assumption, are less volatile than long-duration corporate bonds (9–12 years) or long Treasuries (16–20 years).
Coupon Effect on Duration
Higher-coupon bonds have shorter duration because you get cash back faster. A 6% coupon bond has much shorter duration than a 1% coupon bond of the same maturity, because half your return comes from coupon payments rather than principal appreciation.
This matters enormously in practice. In 2022, when yields surged from 1.5% to 4%, long Treasuries (low coupon, long maturity) suffered devastating losses. Long-duration corporate bonds and high-yield debt did even worse on a price-basis, though some of that was offset by wider credit spreads. Meanwhile, TIPS held up better because their real yield floor kept duration from expanding infinitely.
Using Duration to Size Portfolio Risk
If you manage a bond portfolio with average duration 5 years, you expect:
- A 0.5% yield rise → approximately −2.5% portfolio loss
- A 1% yield rise → approximately −5% portfolio loss
- A 2% yield rise → approximately −10% portfolio loss
These are estimates, because duration is linear and yields don't move in isolation. But they're reliable enough to guide position sizing and rebalancing decisions.
Many investors target a portfolio duration matching their time horizon. If you need the money in 7 years, holding bonds with 7-year duration means your bond portfolio's total return, reinvested, roughly tracks your liabilities. If you hold shorter duration (say, 3 years), you gain flexibility but accept reinvestment risk—future coupons might be reinvested at lower rates. If you hold longer duration (say, 10 years), you lock in capital appreciation potential if rates fall, but face bigger losses if rates rise.
A passive investor holding bond index funds (BND, AGG, VBTLX) typically gets duration around 5–6 years, which is neutral to moderately conservative. A short-term bond fund (SHV, VGSH) offers 1–2 years duration and lower volatility, suitable for money needed in the near term. A long-bond fund (TLT, VGLT) offers 15–17 years duration and much higher volatility, appropriate for investors with very long time horizons and strong conviction that rates will fall.
Why 1% Matters as a Benchmark
A 1% yield change is a standard market move. On an ordinary trading day in equity markets, the S&P 500 might swing 1–2%. For Treasury yields, a 1% move is not extreme—it's the kind of thing that happens within a quarter or two during periods of economic uncertainty or Fed policy shifts.
In 2021, the 10-year Treasury yield was 1.5%. By the end of 2022, it was 3.9%—a 2.4% move, or roughly 2.4× the 1% benchmark. That meant long-duration bonds lost about 2.4× their 1-year estimated loss, compounded by the fact that the relationship becomes non-linear at large moves (more on that later).
Understanding the 1% rule prepares you psychologically. If you're holding a bond position and rates move 1%, you know exactly what to expect. You're not surprised. You can adjust your portfolio with conviction.
Duration and Time Decay
Duration is a snapshot. As time passes and yields don't change, a bond's duration shortens by approximately one year per year of elapsed time. A 10-year bond with 9-year duration today will have roughly 8-year duration a year from now (assuming no coupon reinvestment and stable yields).
This means bond portfolios are self-liquidating. You don't need to actively rebalance for time passage alone; your position naturally shortens duration and reduces interest rate risk as you approach your target horizon.
Practical Application
When you see a bond fund's fact sheet listing duration (often as "effective duration" or "average duration"), that number tells the whole story about interest rate sensitivity. A duration of 8 years on a corporate bond fund means the fund is roughly 8× as volatile as a 1-year Treasury. A duration of 3 years on a short-term bond fund means it's much less affected by rate moves but also has lower yield.
The 1% rule is not perfect—it breaks down for large moves, and it doesn't account for credit spread changes or curve shape shifts. But for quick risk assessment and portfolio construction, it's the single most useful tool in fixed income. Once you internalize that a 5-year-duration portfolio loses 5% when rates rise 1%, you can make sensible decisions about how much interest rate risk you want to carry.
Process Overview
Next
Bond prices respond to yield changes roughly linearly, but that linearity breaks down when yields move by more than 1 or 2 percent. The next article explores large yield shifts and why duration alone becomes an incomplete tool when markets move dramatically.