What Is Duration? Why a “Safe” Bond Fund Can Still Lose You Money
Bonds are supposed to be the boring, sensible part of a portfolio. Then 2022 happened, and the safest bonds on earth fell harder than most people thought possible. One number explains why — and it was printed on the fact sheet the whole time.
By Pavel Penev, MScFounder, TradeWize · 10+ years trading the marketsThe short answer
Duration is a bond's sensitivity to interest rates, measured in years. The rule of thumb is almost rudely simple: if rates rise by 1 percentage point, a bond's price falls by roughly its duration, as a percentage. Duration 3, rates up 1% → price down about 3%. Duration 17, rates up 1% → price down about 17%. It is the single number that decides whether a “safe” bond fund has a dull year or a genuinely horrible one — and it is sitting on the fund's fact sheet right now, waiting for someone to read it.
We are not going to re-explain what a bond is here. If “a bond is a loan where you're the lender” needs a moment to land, our Stocks vs Bonds guide starts from scratch and it's worth two minutes. And we're not doing the credit ladder either — who you lend to, from rock-solid governments down to junk — because our Types of Bonds piece already walks the whole staircase. Both of those are about the same question: how likely am I to be paid back?
This article is about the other dial entirely. Because here is the uncomfortable thing: you can lend to the safest borrower in the world, be repaid every cent exactly as promised, and still watch your investment fall 30% along the way. No default. No drama. No one did anything wrong. That is not credit risk — it's interest-rate risk, and the number that measures it is duration.
Why a bond's price falls when rates rise
Start with the mechanism, because everything else follows from it. Say you lend a government $1,000 for 10 years at 2%. You'll collect $20 a year. Lovely. Now suppose that a year later, interest rates have shot up, and brand-new 10-year bonds are being issued paying 4% — $40 a year on the same $1,000.
Your bond hasn't changed. It still pays $20 a year, and the government will still hand you your $1,000 back at the end. But if you wanted to sell it today, who on earth would pay you full price for a bond paying $20 when they could buy a new one paying $40? Nobody. So they don't pay full price. They pay less — enough less that your measly $20 a year works out to a competitive return on what they paid. Your bond's price falls until its yield matches the new world.
Nothing went wrong. The borrower is fine, the coupon still arrives, the money still comes back. Your bond just got out-competed by a newer one — and the market repriced it accordingly.
That's interest-rate risk in one paragraph. Rates up, prices down. The US securities regulator puts it about as bluntly as a regulator can: when interest rates go up, prices of fixed-rate bonds fall. It's not a market panic or a crisis. It's arithmetic.
Duration is the length of the lever
So rates rising hurts. The obvious next question is: how much? And this is where duration earns its keep, because the answer depends enormously on how long you'd been locked in for.
Think about the bond that matures next year. Rates have jumped, yes, and your bond is now paying below the market rate — but only for twelve more months, and then you get your $1,000 back and can reinvest it at the shiny new rate. The pain is real but brief, so the price barely flinches. Now think about the bond that matures in twenty years. You are locked into the old, worse rate for two entire decades. A buyer has to be compensated for every one of those years, so the discount they demand is enormous.
Same borrower. Same rate move. Wildly different damage — and the only thing that changed was how long the money was tied up. Duration is the number that captures exactly that. Picture a lever bolted down at one end: a rise in rates presses on the far end — the price — and the longer the arm, the further that end falls. Duration is the length of the arm.
Interest rates push with the same force on every bond. What differs is the lever arm — the duration. A 2-year lever barely tips; a 20-year lever swings the price end through the floor.
And the rule of thumb that comes out of it is one of the few pieces of finance maths that is genuinely easy. FINRA — the US brokerage regulator — states it plainly: for every 1 percentage-point change in interest rates, a bond moves in the opposite direction by roughly its duration number, expressed as a percent.
The whole formula
Price change ≈ − duration × change in rates. That's it. A fund with a duration of 6 loses about 6% if rates rise 1%, and gains about 6% if they fall 1%. Multiply, flip the sign, done. You now understand more about bond risk than most people who own bonds.
Set your fund’s duration and how far rates move, and watch what happens to $10,000. The whole calculation is price change ≈ − duration × rate change.
Illustrative. The duration rule is a first-order approximation — real bonds have a little convexity, which softens very large moves. Now tap 2022’s actual shock: duration 6, rates up 2.4 points, and a starting yield of just 1.75%, because rates had spent years near zero. It lands near −13% — the worst year in the Aggregate index’s history, reproduced with one multiplication. And notice why it hurt so much: with almost no yield, there was almost no cushion. Slide the starting yield up to 5% and the same rate shock is far more survivable.
Duration is not maturity (this trips up everyone)
Worth pausing here, because these two get muddled constantly and they are not the same thing. Maturity is simply when the loan ends — a 10-year bond matures in 10 years, and that's a date on a calendar. Duration is a sensitivity: how much the price moves per 1% of rate change. It happens to be quoted in years, which is precisely why people conflate them.
For a typical coupon-paying bond, duration comes out a bit shorter than maturity — because you're getting some of your money back along the way, in coupons, rather than all of it at the end. A 10-year bond might have a duration of around 8. The bigger the coupon, the more cash arrives early, and the shorter the duration. A zero-coupon bond, which pays you precisely nothing until the day it matures, has a duration equal to its maturity — it is the purest, most rate-sensitive instrument of the lot.
Maturity
When you get your money back
- A date. The loan ends, the principal is repaid.
- A 10-year bond matures in 10 years. No interpretation required.
- Tells you nothing directly about how far the price can swing.
Duration
How hard the price swings when rates move
- A sensitivity, confusingly quoted in years.
- Duration 8 → a 1% rate rise costs you roughly 8%.
- Usually a bit less than maturity, because coupons pay you back early.
Learn it by doing
Reading about it is one thing — it clicks when you do it. Practise this hands-on in a free, interactive lesson (Stage 4: Stocks, Bonds, Cash & Alternatives).
Try the free lesson →2022: the year the seatbelt had a lever attached
All of this stayed comfortably theoretical for about forty years, because rates spent most of that time drifting downward, which quietly made bond investors money. Then came 2022. Inflation surged, and the Federal Reserve raised its policy rate from near zero to a range of 4.25–4.50% — 4.25 percentage points in a single calendar year, the most aggressive tightening in decades.
The Bloomberg US Aggregate — the broad, sensible, boring index that sits inside most “total bond market” funds — fell about 13% that year. That was its worst year since the index began in 1976, comfortably beating the previous record. Millions of people watched the safe half of their portfolio, the ballast, the seatbelt, do the one thing it was explicitly there not to do.
Look carefully at those three numbers, because they are the whole article in one row. All three are US government debt. The credit quality is identical — the safest borrower on the planet, and not one of them missed a payment. The only difference between losing 3.9% and losing 31.2% was duration.
Calendar-year total returns, 2022. Short-dated Treasuries (duration ~2), the broad Aggregate index (~6), and long-dated Treasuries (~17). Nobody defaulted. The Fed simply raised rates 4.25 points, and each fund fell in proportion to its lever.
The rule of thumb predicted it almost exactly
Try it yourself. The Aggregate index had a duration of roughly 6, and the market yields that price it rose about 2.4 percentage points over 2022. The formula says: −6 × 2.4 ≈ −14% in price. Then add back the interest the bonds actually paid you along the way — and here's the sting: that was only about 1.75%, because rates had spent years pinned near zero. So −14% plus a 1.75% cushion lands you near −13%, which is, to within a rounding error, exactly what happened. The worst year in the index's history was not a mystery. It was a multiplication.
And that thin cushion is the underrated half of the story. A bond's yield is the shock absorber that offsets a price fall — but after a decade of near-zero rates, there was barely any yield left to absorb anything. Investors were holding an asset with a long lever and no padding. Run the same 2.4-point shock today, against yields of 4-5%, and the same fund has a materially better year. Ironically, the thing that made 2022 so painful — rock-bottom yields — is the very thing 2022 fixed.
The bit that actually matters: a bond fund never matures
Here's the distinction that decides whether 2022 was a flesh wound or a genuine loss, and it's the one most people never had explained to them.
If you own an individual bond and you simply hold it to maturity, the price wobble is largely theatre. Your bond might be marked down 20% in the middle of its life, but as the maturity date approaches, its price is dragged inexorably back toward the $1,000 you're owed — traders call this the pull to par. On the final day, you get your $1,000. You collected every coupon. Your loss on paper evaporated, because you never sold. The only thing rising rates truly cost you was the opportunity to have lent at the better rate instead.
A bond fund does not do this. A bond fund has no maturity date, because it isn't a bond — it's a rolling basket of hundreds of them. As its holdings age, the manager sells them and buys new ones to keep the fund's duration roughly constant. There is no date in the future on which the fund hands you your money back at par. There is no pull to par. There is only the price, every day, reflecting what the basket is currently worth.
Left: a single bond dips when rates rise, then is dragged back to its $1,000 face value as maturity approaches. You are made whole. Right: a fund holds a rolling basket with no end date — the dip is simply the new price. It recovers by earning the now-higher yields, not by maturing.
This is not an argument against bond funds, and it would be daft to read it as one — funds give you diversification across hundreds of borrowers for a few basis points, and buying individual bonds is fiddly work most people should not take on. But it does mean the reassurance “just hold to maturity and you'll be fine” does not apply to the thing most people actually own. There is no maturity to hold to.
The good news, and it is genuinely good news, is that a bond fund heals in a different way. Once rates have risen, the fund is buying new bonds at the new, higher yields. Your income goes up. Given roughly a duration's worth of years, that fatter income stream typically makes up for the price hit — which is a rather elegant fact: hold a bond fund for about as long as its duration, and rising rates broadly stop being your enemy. A duration of 6 hurts today and pays you back over about six years. Investors who sold their bond funds in disgust in late 2022 locked in the loss and then handed the recovery to whoever bought them.
So what duration should you actually own?
The honest answer is: roughly match your duration to when you need the money. That's the whole discipline. Cash you need next year has no business sitting in a fund with a duration of 17, because a bad rate year could take a fifth of it. Money you won't touch for a decade can happily ride an intermediate fund, because you'll be around long enough for the higher yields to do their repair work.
| Fund type | Typical duration | A +1% rate rise costs roughly | What it's actually for |
|---|---|---|---|
| Ultra-short / money market | Under 1 year | Under 1% | Parking cash you may need imminently |
| Short-term bond | 2–3 years | 2–3% | Money you'll want within a few years |
| Intermediate / total bond market | About 6 years | About 6% | The core ballast in most portfolios |
| Long-term / long Treasury | 15–20 years | 15–20% | Rate bets and pension-style liability matching |
Durations are typical, not fixed — look up your own fund's number. FINRA's advice is refreshingly practical: it's on the fund's fact sheet, under “Key Facts” or “Portfolio Data.” It takes about ten seconds to find, and almost nobody looks.
And one last caveat, straight from FINRA, that deserves repeating: a low duration does not mean low risk. Duration only measures rate sensitivity. A short-dated junk bond has a tiny duration and can still hand you a catastrophe, because the borrower may simply not pay you. Duration and credit quality are two separate dials, and a bond can go wrong on either — which is exactly why we wrote about the credit ladder separately.
Frequently asked questions
What is duration in simple terms?
Duration measures how much a bond's price moves when interest rates change. It's quoted in years, and the rule of thumb is that a 1 percentage-point rise in rates drops the price by roughly the duration number, as a percentage. A duration of 5 means a 1% rate rise costs you about 5%. A duration of 15 means it costs you about 15%.
What is the difference between duration and maturity?
Maturity is a date — when the loan ends and you get your money back. Duration is a sensitivity — how far the price swings per 1% of rate change. Duration is usually a little shorter than maturity, because coupon payments return some of your money early. A zero-coupon bond, which pays nothing until the end, has duration equal to its maturity.
Why do bond prices fall when interest rates rise?
Because newly issued bonds start paying more. Your existing bond is locked into the old, lower rate, so nobody will buy it at full price when they could buy a new one paying more. Its price drops until the return a buyer gets matches what's available elsewhere. The borrower hasn't done anything wrong — your bond has simply been out-competed.
How do I calculate what a rate rise will cost me?
Multiply the duration by the rate change and flip the sign. A fund with a duration of 6, if rates rise 0.5%, falls roughly 6 × 0.5 = 3%. If rates fall 0.5%, it gains roughly 3%. It's a first-order approximation, so it gets slightly less accurate for very large moves, but for everyday purposes it's remarkably good.
Why did bond funds lose money in 2022?
The Federal Reserve raised rates by 4.25 percentage points in one year, from near zero. Because bond prices move opposite to rates, and by an amount set by duration, every bond fund fell in proportion to its duration. The broad Bloomberg US Aggregate fell about 13% — its worst year since 1976 — while long-dated Treasury funds fell over 30%. No borrower defaulted; it was purely rate risk.
Does duration matter if I hold to maturity?
For an individual bond, much less — as maturity approaches its price is pulled back to face value, so if you never sell you get your principal back and collect every coupon. But a bond fund has no maturity date; it holds a rolling basket and keeps its duration roughly constant. There is no pull to par. A fund instead recovers by reinvesting at the new, higher yields, which typically takes about as many years as its duration.
What is a good duration to have?
Broadly, match duration to when you need the money. Cash needed within a year or two belongs in ultra-short or short-term funds, where a rate shock costs you very little. Money you won't touch for a decade can sit in an intermediate fund with a duration around 6, because you'll be invested long enough for higher yields to repair any price hit. Long-duration funds are a deliberate bet on falling rates, not a default choice.
What is the difference between Macaulay duration and modified duration?
Macaulay duration is the weighted-average time until you receive a bond's cash flows — a genuine measure in years. Modified duration adjusts it slightly and is the one that gives you the price-sensitivity rule of thumb. When a fund fact sheet quotes “duration,” it almost always means modified (or effective) duration, so you can use the multiply-and-flip rule directly.
Does a low duration mean a bond is low risk?
No — and FINRA makes a point of saying so. Duration only measures interest-rate sensitivity. A short-dated high-yield bond has a low duration and can still lose you everything if the borrower defaults. Credit risk and rate risk are separate dials. A bond can be safe on one and dangerous on the other.
So: duration is the lever. It is one number, it is printed on every bond fund's fact sheet, and it tells you, with unnerving accuracy, how bad a rising-rate year is going to be for you. It explained 2022 to the decimal point, and it will explain the next one too. The people who were blindsided by their “safe” fund falling 13% were not the victims of anything mysterious. They just hadn't read the number.