Most investors own bonds. Very few can say how hard those bonds will move when interest rates do. One number answers that, and reading it takes about four minutes to learn.
Ask someone what they own in bonds and you will hear a fund name, maybe a yield. Ask what happens to that position if rates rise one percent and the conversation usually ends. Which is strange, because the answer is printed on every fund fact sheet, in one number: duration.
The working definition: duration is how many percent your bond position moves when rates move one percent, in the opposite direction. A fund with a duration of 6 falls roughly 6% when rates rise one point, and gains roughly 6% when they fall one point. That is the whole trick. Everything else is refinement.
A bond is a promise of fixed payments. Once you own it, those payments never change; what changes is what everyone else can get. If you hold a bond paying 4% and new bonds start paying 5%, nobody will buy yours at full price. Its price drops until its remaining payments compete with the new rate. The longer you are stuck waiting for those fixed payments, the bigger the discount has to be. That waiting time, weighted by when each payment arrives, is duration. Long wait, big sensitivity. Short wait, small.
A 10-year bond does not have a 10-year duration. Coupons arrive along the way, and every payment you receive early shortens the effective wait. A 10-year Treasury paying a healthy coupon has a duration closer to 8. A zero-coupon bond, which pays everything at the end, is the one case where duration equals maturity, which is exactly why zeros are the most violent bonds you can own.
Duration is not a risk to minimize. It is a dial, and it should be set to match when you need the money.
If the math feels abstract, 2022 made it concrete. Rates rose roughly three points, and long-term Treasury funds, duration around 17, lost about a third of their value. Not because anyone defaulted. The bonds were doing exactly what the math said: 17 times 3 is a 50% move in theory, softened in practice by the curve and convexity, but devastating either way for anyone who thought "Treasuries" meant "safe." They were safe from default, not from duration. Investors in short-term funds barely noticed the same year.
The classic answer is matching: hold duration roughly equal to when you need the money. Spending the cash in two years? A duration near two means rate moves roughly wash out over your actual horizon. Funding a liability fifteen years away? Long duration is not a gamble, it is a lock on today's rate for the whole wait. The common mistake runs in both directions: retirees holding long-duration funds for money they spend next year, and thirty-year-horizon investors hiding in cash equivalents, reinvesting at whatever each year happens to offer.
The second answer is the job within the portfolio. Long duration is the piece most likely to rally hard in a growth scare, which is when equities are falling; that negative correlation, when it shows up, is why duration earns a seat even for investors who need nothing from bonds for decades. It does not always show up. 2022 was the year stocks and long bonds fell together, and the reminder that the hedge is a tendency, not a contract.
We treat duration as a decision, not a default. Reserve cash and near-term spending sit at the short end, deliberately boring. The long-horizon sleeve carries duration sized to the job it is hired for, whether that is liability matching or crash ballast, and we read the fund's stated duration before buying, because two funds with the same name can carry very different numbers. None of this requires forecasting rates. It requires knowing your number, and knowing why it is set where it is.
For informational and educational purposes only. Duration figures are approximations; actual price behavior depends on convexity, credit, the shape of the yield curve, and market conditions. Historical episodes are illustrative, not predictive. This is not personalized investment advice.
Do you know the duration of your bond sleeve, and the reason it is set there? If the answer to either half is no, that is a ten-minute conversation worth having.
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