A bond issued at a 5 percent coupon pays $50 annually on $1,000 principal. If market rates rise to 8 percent, new issuance yields $80 annually. The old bond's $50 coupon now trades at a discount—its price falls below $1,000 to match the yield of fresh debt.
This is the inverse relationship that dominates fixed-income markets: rates up, prices down. A 100-basis-point move can swing a $1,000 bond by $80 or more, depending on duration.
Duration—the weighted average time to receive a bond's cash flows—is the metric that quantifies this sensitivity. A 10-year bond with a 5 percent coupon has a duration of roughly 8 years. For every 1 percent move in yield, that bond's price moves approximately 8 percent in the opposite direction. In practical terms: if the 10-year yield jumps from 4 percent to 5 percent, an investor holding that bond faces a loss of 8 percent on mark-to-market.
Conversely, when rates decline—say from 5 percent to 3 percent—that same bond becomes more valuable. Its $50 annual coupon now outpaces new issuance at 3 percent, so its market price rises above $1,000. The price gain mirrors the duration exposure that hurt when rates climbed.
For institutional portfolios, managing duration is survival. A pension fund or insurance company that needs to match liabilities decades in the future cannot ignore the risk that rising rates crush the value of long-dated bonds in its portfolio. If rates climb before a planned liability is due, the fund faces a choice: sell at a loss or hold and wait for maturity. Most hold, but the opportunity cost compounds.
Credit ratings signal repayment risk and heavily influence yield. An AAA-rated sovereign bond or corporate trades at lower yields than a BBB name because default risk is lower. Spread compression—when credit spreads narrow—means risk premiums shrink. In a bull steepener (long rates rise, short rates hold), credit spreads often widen because investors demand more return for duration and credit risk combined. In a bear flattener (short rates rise faster than long rates), spreads compress as flight-to-quality flows and technical positioning dominate.
Some bonds compensate through price appreciation rather than coupons. Treasury bills and zero-coupon bonds are sold at a discount and mature at face value; the difference is the yield. A 52-week bill bought at $980 and redeemed at $1,000 generates 2.04 percent yield. These instruments exhibit extreme duration sensitivity because all cash flow arrives at maturity—no interim coupons smooth the path.
The yield curve itself encodes duration expectations. When the 2-10 spread inverts (short rates above long rates), market participants are pricing recession and future rate cuts. When it steepens, growth expectations and inflation repricing take hold. Portfolio managers positioned for a steepener (long the 10-year, short the 2-year) benefit if long rates fall relative to short rates—but pay the price if the curve flattens. This is duration positioning in real time.
For investors facing multiple rate cycles, the mechanics are simple but unforgiving: duration risk is systemic in bonds. A 1 percent move in yield is not a small move—it is 1 percent of $1 trillion in aggregate U.S. bond market value every time it happens. The Treasury market alone trades $650 billion per day. When duration moves that fast, capital flows violently.
