Bonds and Interest Rates: Understand Price Changes
Separate the coupon from yield to maturity and understand why a bond’s price responds to market rates.
In this article
The first loss on a bond fund always surprises. How can a supposedly prudent investment fall 7%? The answer lies in price mechanics. The coupon, the interest promised at issue, never moves. It is the security's price that adjusts when market rates change, since nobody pays full price for a 2.5% bond when new issues offer 4.5%. Sensitivity is measured by duration: with nine years of duration, the decline is roughly 9% per point of rate increase, while a short duration barely moves. Add to that credit risk, a separate matter, and the difference between holding a bond to maturity and holding a fund that rolls its holdings continuously. This article takes the mystery apart piece by piece. It shows how to align duration with your horizon and how to read a paper loss without obeying it. The mismatch between product and calendar is often the part you can fix.
Separate the coupon from the yield to maturity
A bond carries two numbers that people often confuse. The coupon is the interest promised at issue, fixed forever. The yield to maturity is what the security actually returns when bought at its current price. When prices move, the coupon stays the same and the yield to maturity adjusts. A bond with a 2.5% coupon bought below par returns more than its coupon, the difference coming from the gain at maturity. This distinction explains the bond market's paradoxes: a fund that just lost 7% suddenly shows a higher yield to maturity, because falling prices raised the return for buyers. The coupon describes the security's past, and the yield to maturity describes its future. That is the one you compare.
Understand the price-rate seesaw
A bond's price and market rates move in opposite directions, by simple arithmetic. Nobody pays full price for a 2.5% coupon when new issues offer 4.5%, and the old bond's price falls until the yields equalize. The seesaw works both ways: a rate cut pushes up the prices of existing bonds. This mechanism is neither a flaw nor a danger signal. It is the normal operation of a market where payment promises trade at the day's price. The loss displayed on a bond fund after a rate rise reflects that adjustment, not borrower defaults. The coupons keep arriving and the securities keep being repaid at maturity.
Read duration as the sensitivity gauge
A security's or fund's sensitivity to rate moves is summarized in one published number: duration. In practice, a nine-year-duration fund loses about 9% per point of rate increase, and gains as much per point of decrease. A two-year duration barely moves. You find duration in the fund facts, and it guides the match with your horizon. Choose short duration for money needed in the coming years, where stability comes first. Choose long duration for distant horizons, where the sensitivity is tolerable and the higher yields compound. Mismatch is the true source of bond surprises. A long-duration fund held in short-term savings does exactly what it promises, at the wrong moment.
Distinguish held bond from fund, credit from rates
Two distinctions complete the reading. First, holding a bond to maturity eliminates price risk, since repayment at par erases the interim fluctuations. A bond fund, by contrast, has no single maturity. Its holdings roll continuously and its value tracks the market all the time, which changes how its declines should be read. Second, rate risk is not credit risk. The first moves prices without threatening repayment. The second, the issuer's solvency, threatens repayment itself and is compensated through the yield spread on lower-quality securities. Choose a bond portfolio on both axes: duration by horizon, credit quality by function, either a stability cushion or a return engine.
Quebec scenario
A machinist in Sorel-Tracy buys a bond ETF believing it as stable as a GIC. Six months and two rate hikes later, the position shows -7% and he cannot understand how bonds lose value. His advisor explains. The coupon, the interest promised at issue, never moved. The price fell, because nobody pays full price for a 2.5% bond when new issues offer 4.5%. The yield to maturity of his fund has actually risen. Sensitivity depends on duration. His ETF, at nine years, loses roughly 9% per point of rate increase, while a short-duration bond fund would barely have moved. There is also credit risk, a separate matter, and the difference between holding a bond to maturity and having to sell it early. He reorganizes around his real horizons: short duration for money needed within five years, long duration only for the retirement slice. The paper loss stops being a riddle. It was the price of a product mismatched to his calendar, and that mismatch, rather than the market, was the part he could fix.
Checklist
- Separate the coupon from yield to maturity
- Understand the price's reaction to rates
- Record each held fund's duration
- Estimate the sensitivity per rate point
- Align duration with the money's horizon
- Check credit risk separately
- Distinguish a bond held to maturity from a fund
- Read a paper loss without obeying it
- Reorganize by horizon rather than by fear
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