The Confusing Math of Bonds
Stocks and bonds seem to behave alike on a brokerage screen: prices bounce around, and you can watch your holdings go up and down. But the physics underneath is different, and it changes how you should feel.
When a bond's price falls, its yield rises. That is not incidental — it is the same sentence in two languages. The yield is what a new buyer earns going forward. So the investor who bought earlier has an unrealized mark-to-market drop, while a brand-new buyer receives a higher starting income. Two investors, same bond, opposite experiences.
What Duration Really Measures
Duration is the number that connects the two. Roughly, it says: for every 1% move in interest rates, a bond's price moves by duration percent in the opposite direction. A 7-year-duration fund loses about 7% if rates rise 1% — and gains 7% if they fall.
That number also tells you how quickly you recover from a rate shock. Ride a 1% hike on a 7-year bond and, all else equal, your higher reinvested income makes you whole in roughly seven years. The bond's income jumped; the price drop is just the present value adjusting.
The Long Game of Bond Ladders
This is why a bond "loss" is different from an equity loss. Equities can gap down and never return — companies can die. Bonds, held to maturity, pay back par. Price volatility on bond funds is a timing feature, not a permanent impairment.
A duration-matched strategy — where bond maturity roughly equals the horizon of the money it holds — lets you ignore price noise entirely. The yield at purchase becomes the yield you effectively earn, all ride-through aside.
Why the Yield Curve Matters
Short rates and long rates rarely move together. An inverted curve (short rates above long rates) often signals markets expecting an economic slowdown. When that happens, longer bonds can rally exactly as equities struggle — the diversification working as designed.
If rates rise further relative to your expectations, it costs you on price but pays you on income, and the reinvestment starts earning more. Laddered investors treat rising rates not as bad news but as a raise.
The Takeaway
When you see a news headline about falling bond prices, ask one question first: "What happened to yields?" If yields rose, bond investors' future income just went up. A 4% yielding treasury pays twice the income of a 2% one — and the portfolio that lives long enough to reinvest earns the difference. Patience is built into the asset.