Duration Sensitivity Rule
Estimate a bond’s price response before interest rates move
- Difficulty
- Easy
- Time to result
- ~days to results
- Steps
- 5
- Confidence
- 97%
Duration converts interest-rate exposure into an approximate price response. Start with the published duration of a bond or fund, then multiply it by the contemplated change in rates: a five-year duration and a one-percentage-point rate increase imply roughly a five-percent price decline. A comparable decline in rates implies an approximate gain, with longer-duration holdings moving more than shorter-duration holdings. Because a portfolio’s headline duration is only an average, investors can refine the assessment by examining key-rate durations at different points of the yield curve and credit-spread duration. The resulting estimate is not a precise forecast, but it provides a consistent way to compare alternatives, quantify downside, and align fixed-income risk with portfolio objectives.
Origin
Extracted from Masters in Business during Karen Vera’s explanation of how investors can quantify interest-rate risk in bonds and bond funds.
Core principles
- 01Duration measures a bond’s sensitivity to interest-rate changes.
- 02Price and interest rates generally move in opposite directions.
- 03Longer duration creates larger price movements.
- 04Published duration is an estimate for the bond or portfolio as a whole.
- 05Key-rate and credit-spread durations reveal risks hidden by one average.
How to run it
- 1
Locate the duration
Find the published duration for the bond or bond fund. Treat it as the portfolio’s approximate sensitivity to a one-percentage-point change in rates.
Pro tip Use the provider’s current fact sheet rather than an old purchase document.
Watch out Duration can change as securities mature or the portfolio manager trades.
- 2
Define the rate scenario
Select a realistic upward or downward interest-rate move to test. Express the move in percentage points so it can be applied consistently.
Pro tip Test several scenarios instead of relying on one rate forecast.
Watch out Different maturities may not experience the same rate change.
- 3
Estimate the price response
Multiply duration by the rate change to estimate the percentage price movement. Use the opposite direction: rising rates imply falling prices, while falling rates imply rising prices.
Pro tip A duration of five makes a one-point rate move easy to interpret as an approximate five-percent price move.
Watch out The relationship is an approximation and becomes less precise for large rate changes.
- 4
Inspect concentrated exposures
Review key-rate durations to see whether risk is concentrated around two-, five-, ten-, twenty-, or thirty-year rates. Review credit-spread duration when the holding contains meaningful credit risk.
Pro tip Compare funds with similar headline duration to uncover different yield-curve exposures.
Watch out Headline duration alone can conceal materially different sources of risk.
- 5
Match risk to purpose
Compare the estimated price movement with the holding’s intended role and your tolerance for temporary losses. Shorten duration if the downside is unacceptable or retain longer duration when its potential appreciation and hedging role are appropriate.
Pro tip Evaluate duration as part of the entire portfolio rather than in isolation.
Watch out Do not treat longer duration as a free source of additional yield.
In the wild
An investor reviews a bond fund with a duration of five and tests a one-percentage-point rate increase. The rule indicates an approximate five-percent price decline, allowing the investor to decide whether the fund’s income and diversification benefits justify that risk.
→ The investor makes the bond allocation with an explicit loss estimate rather than relying only on yield.
A portfolio owner compares a short-duration Treasury fund with a twenty-plus-year fund. Applying the same rate scenario shows that the long-duration fund could move much more sharply, making it better suited to a deliberate hedge than to near-term spending reserves.
→ Each fund is assigned a role consistent with its expected volatility.
Common mistakes
Reading duration as maturity
Duration measures price sensitivity and is not simply the number of years until a bond matures. Confusing the two can produce a poor estimate of interest-rate risk.
Ignoring the direction of rates
Bond prices generally move opposite to interest rates. Applying the estimated percentage change in the same direction reverses the framework’s meaning.
Relying only on average duration
A portfolio-level average can hide concentrated exposure at particular maturities or to credit-spread changes. Use more granular duration measures when they are available.
Is it for you?
Best for
It is best for investors comparing bond funds or stress-testing fixed-income exposure before a change in rates.
Not ideal for
It is not ideal as an exact price forecast when yield-curve shifts, credit spreads, or bond convexity materially affect returns.
From the transcript
“So duration is simply the interest rate risk of a bond,”
“if interest rates go up by one percent, that bond will drop in value by five percent.”
“duration is a helpful measure for at least quantifying the loss that they could have from changes in rates.”
From the episode
Team Favorite At the Money: Managing Bond Duration