Why Bond Prices Fall When Rates Rise

You've probably heard bonds called a safe asset. And yet in 2022, a long-duration US Treasury ETF dropped almost 30% in one year. In Korea, the 30-year government bond ETF took a similar hit. A "safe asset" that fell harder than stocks looks confusing at first. Let's walk through why bond prices fall when rates rise, starting from the basic mechanism.

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What is a bond, really?

Start with the product. A bond is essentially an IOU. A government or company says "lend us your money now, and we'll pay back 10,000 won in 10 years with 5% interest each year." Buy that IOU and you collect set interest each year, then get the principal back at maturity.

Two things define a bond: the interest rate and the maturity. The rate is what percentage you get each year. Maturity is when you get the principal back. The rate locked in at issuance is called the coupon rate, and it doesn't change for the life of the bond.

Here's where it gets confusing. Bonds can be bought and sold in the market after issuance. The bond you bought can be sold to someone else before maturity. That trading price changes every day — because market rates move.

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So what happens when market rates rise?

This is the trickiest part. Bear with me for a moment.

Say last year you bought a 10-year government bond with a 3% coupon, for 10,000 won. You collect 300 won in interest each year. Today, a brand new 10-year government bond gets issued at a 5% coupon. The new one pays 500 won a year.

Could you sell those two bonds at the same price in the market? Of course not. Who would pay the same price for a bond that pays 300 a year when there's another one paying 500 sitting right next to it?

So your 3% bond has to drop in price for it to actually trade. Smaller annual interest means you have to sell it cheap enough that the total return becomes comparable to the new bond. The market quietly marks the price down. That's the mechanism behind "when rates rise, existing bond prices fall."

The reverse works the same way. If market rates drop to 1%, your 3% bond suddenly becomes attractive. Getting 300 a year is much better than the market average of 100. So your bond's price moves up.

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Why duration matters

The unit that measures how sensitive a bond's price is to rates is called duration. It's expressed in years.

A bond with a 5-year duration roughly drops 5% in price when rates rise 1%. A bond with a 30-year duration drops about 30% in price for the same 1% move. The longer the duration, the more violently the price swings for the same rate move.

Why? A longer duration means the cash you'll receive sits farther out in the future. When market rates change, the rate you use to convert that future cash to present value changes too. The farther out the money, the more the change compounds.

The 2022 case made this brutally clear. The Fed hiked the policy rate more than 4 percentage points in a single year. Short-duration bond ETFs ended with single-digit losses, but the long-duration US 20-year Treasury ETF (around 17 years of duration) fell almost 30%. Same bond category, but duration alone split the losses dramatically.

Korea ran the same script. The 30-year government bond ETF took the worst hit, while the 3-year and 5-year ETFs got off much lighter.

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So are bonds risky?

This is where balance matters. Bonds themselves haven't become risky. The risk lies in not knowing your duration.

If you hold a bond to maturity, you collect the set principal and interest. As long as the issuer doesn't default, that promise holds. Investors who bought bonds with a hold-to-maturity strategy didn't actually lose money in 2022 — only the mark-to-market value moved. The principal still gets returned at maturity.

The trouble is with bond ETFs. ETFs don't have a maturity date. They sell bonds approaching maturity and buy new ones to keep the fund's duration roughly constant. So the duration shown when you buy the ETF is the price sensitivity you're inheriting. There's no maturity to wait out. Sell after a price drop and that loss locks in.

If you're buying a bond ETF, check two things first. One, the ETF's duration. Two, your view on rates. If you expect rates to rise further, short-duration ETFs swing less in price. If you expect rates to fall, long-duration ETFs move more on the upside.

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Are long-duration ETFs a weapon during cutting cycles?

This is bonds' other face. When rates fall, long-duration ETFs see the biggest price moves up.

The same 30-year duration bond that loses ~30% on a 1% rate rise also gains ~30% on a 1% rate drop. A 30% price move in a year also means you're carrying the matching duration risk on the way down. That's why long-duration ETFs attract attention right at the start of a real cutting cycle.

Early 2026 looked like that moment. When the Fed signaled additional cuts, capital flowed into long-duration ETFs. People weren't simply buying a safe asset — they were using an instrument that swings hard on rate direction.

The phrase "bonds are safe" is only half true. With a hold-to-maturity strategy, bonds are safe. In ETF trading, they're assets that move sharply with rate direction. The risk profile completely changes based on how you actually enter.

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Wrapping up in one line

Bond prices and market rates move opposite each other because new bonds compete with old ones. The size of the swing scales with duration. Hold-to-maturity is independent of mark-to-market. ETFs inherit duration directly as their price sensitivity.

Next time bond news lands, look at just two things: which way rates are heading, and what the ETF's duration is. Their product roughly determines your P&L. The risk isn't bonds — it's buying bonds without knowing your duration.