Fixed Income
Maturity Effect: Why Bonds Behave Differently as They Age
There’s a pattern in fixed income that every bond investor encounters eventually, even if they don’t always have a name for it. A long-dated bond swings violently when interest rates move. That same bond, ten years later, barely flinches at the same rate. The bond didn’t change in any fundamental sense. The issuer is the same, the coupon is the same, the credit quality is similar. What changed is how much time is left until maturity. And that turns out to matter enormously.
This is the maturity effect and while it sounds like a straightforward observation, its implications run deep into how fixed income portfolios are managed, how duration works in practice, and how bond pricing behaves in ways that aren’t always intuitive.
Start With What We Already Know About Duration
Duration is the standard measure of a bond’s sensitivity to interest rate changes. A bond with a duration of 7 will lose approximately 7% in price for every 1% rise in yields, and gain approximately 7% for every 1% fall.
The longer the time to maturity, generally, the higher the duration. A 30-year bond has far more duration than a 2-year bond with the same coupon and credit quality. This makes intuitive sense: cash flows that are further away are discounted more heavily, so a change in the discount rate affects their present value more dramatically.
But here’s the part that the maturity effect specifically addresses: duration doesn’t stay constant. As a bond ages as its maturity shortens with each passing day its duration falls. And as duration falls, its price sensitivity to interest rate changes falls with it.
This isn’t passive or gradual in some uniform way. The relationship between maturity and duration and therefore between maturity and price volatility has a specific shape, and understanding that shape is what the maturity effect is really about.
What the Maturity Effect Actually Says
The maturity effect describes how a bond’s price volatility changes as it approaches maturity.
The core observation is this: as a bond gets closer to its maturity date, its price becomes progressively less sensitive to changes in interest rates. The closer to maturity, the smaller the price swing for a given yield move.
At the extreme, consider a bond with one day left until maturity. Its price is essentially fixed at par or very close to whatever the redemption value is. No interest rate move in the world will change what you’re going to receive tomorrow. Price sensitivity is effectively zero.
At the other extreme, a 30-year bond is massively sensitive to yield changes because so many of its cash flows coupons stretch over three decades, plus the principal at the end are being discounted over long time horizons. A small change in the discount rate gets compounded over 30 years of cash flows.
Everything in between sits on a spectrum. As maturity shortens, sensitivity falls. That’s the maturity effect.
The Pull to Par
Closely related to the maturity effect and in many ways the same phenomenon viewed from a price perspective rather than a sensitivity perspective is the concept of pull to par.
A bond trading at a discount (price below face value) will gradually rise toward par as it approaches maturity. A bond trading at a premium (price above face value) will gradually fall toward par. This movement happens regardless of what interest rates do; it’s a mechanical consequence of how bond pricing works.
Why? Because at maturity, the bondholder receives exactly the face value full stop. That’s what the contract says. So if the bond is trading at 92 today and matures in three years, something must bridge the gap between 92 and 100 over those three years. That bridging is the pull to par, and it creates a predictable component of return the capital gain (for discount bonds) or capital loss (for premium bonds) that accrues as maturity approaches.
The maturity effect and pull to par are two sides of the same coin. Falling price sensitivity as maturity approaches is the duration story. Convergence toward face value as maturity approaches is the price story. Both are driven by the same underlying reality: the bond’s final payment is fixed, and time is running out.
Why This Creates Asymmetric Behaviour
Here’s where it gets genuinely interesting for portfolio management.
A bond that has been in a portfolio for several years is not the same instrument it was when it was purchased not in terms of its risk profile, at least. If you bought a 10-year bond five years ago, you now hold a 5-year bond. Its duration has fallen. Its sensitivity to rate moves has fallen. Its behaviour in the portfolio is different.
This matters for a few reasons.
First, portfolios that are not actively managed will see their duration drift downward over time purely because of the maturity effect. A portfolio built to match a liability profile or benchmark duration needs to be rebalanced; bonds need to be sold and replaced with longer-dated issues just to stand still in duration terms.
Second, the maturity effect interacts with the yield curve in ways that affect relative value. Short-dated bonds are less volatile, which is why they typically offer lower yields investors accept less compensation because they’re bearing less risk. Long-dated bonds offer higher yields as compensation for greater volatility. This is one of the explanations for the normal upward slope of the yield curve.
Third, for investors managing duration actively trying to position the portfolio for rate moves they expect the maturity effect means that a long position in a 20-year bond is a very different bet than a long position in a 5-year bond, even if the current yield difference doesn’t fully reflect the difference in volatility.
Zero-Coupon Bonds: Where the Maturity Effect Is Most Visible
The maturity effect is most cleanly observed in zero-coupon bonds, because there’s only one cash flow the principal at maturity and therefore no ambiguity about what’s being discounted.
A zero-coupon bond’s duration is equal to its maturity. A 10-year zero-coupon bond has a duration of exactly 10. A 5-year zero has a duration of exactly 5. As time passes and maturity shortens, duration falls one-for-one with time. The maturity effect here is perfectly linear.
For coupon-bearing bonds, it’s slightly messier because intermediate coupon payments reduce duration below the bond’s stated maturity; coupons effectively pull some of the cash flows forward in time, reducing the average weighted timing of payments. But the direction is the same: duration falls as maturity shortens, just not at a one-for-one rate.
This is why zero-coupon bonds are the purest expression of interest rate risk among fixed income instruments, and why they’re often used to construct duration-matched portfolios or immunisation strategies; their duration is known precisely and predictably at every point in time.
The Maturity Effect and Convexity
Duration is a linear approximation of the relationship between yield changes and price changes. But the actual relationship is curved and that curvature is what convexity captures.
The maturity effect has a convexity dimension too. Longer-dated bonds generally have higher convexity than shorter-dated bonds. Convexity is a desirable property it means that price gains from falling yields are larger than price losses from rising yields of the same magnitude. As a bond ages and its maturity shortens, convexity falls along with duration.
For a portfolio manager, this means that an ageing bond portfolio is losing not just duration but also convexity and the asymmetric upside that long-dated bonds provide. Again, active rebalancing is required to maintain the intended risk profile.
Immunisation and the Maturity Effect
One of the most direct applications of the maturity effect in portfolio management is immunisation constructing a bond portfolio so that its value is protected against interest rate changes over a specific horizon.
The classic immunisation condition requires that the portfolio’s duration equals the investment horizon. If this condition is met, the capital loss from rising rates (price effect) is approximately offset by the reinvestment gain from reinvesting coupons at higher rates and vice versa for falling rates.
But immunisation is not a set-and-forget strategy. Because of the maturity effect, duration falls as time passes. The investment horizon also shortens but not necessarily at the same rate as the portfolio’s duration. The manager needs to rebalance periodically to keep duration matched to the horizon.
This dynamic rebalancing requirement is a direct practical consequence of the maturity effect. It’s why pension funds and insurance companies with long-duration liabilities spend considerable effort actively managing duration not because their target changes, but because the maturity effect continuously erodes the duration of the assets they hold.
An Indian Market Illustration
Consider an investor who buys a 10-year Government of India bond at issuance currently yielding around 7%. At the time of purchase, the bond might have a duration of roughly 7-7.5 years. A 100 basis point rise in yields would translate to roughly a 7-7.5% fall in price.
Five years later, that same bond is now a 5-year bond. Its duration has fallen to perhaps 4-4.5 years. The same 100 basis point rise in yields now translates to roughly a 4-4.5% fall in price meaningfully less than before.
The investor holding this bond is now exposed to much less interest rate risk than they were when they bought it. If they originally bought it to gain duration exposure, perhaps expecting rate cuts and rates haven’t moved as anticipated, the maturity effect has been quietly reducing their bet for five years.
If they still want the same duration exposure, they need to sell the seasoned bond and buy a new 10-year or find some other way to restore duration. That’s the practical implication of the maturity effect in a real portfolio.
Key Takeaways for the Exam
The maturity effect describes how a bond’s price sensitivity to interest rate changes decreases as the bond approaches maturity. Duration falls as maturity shortens a bond aging in a portfolio is continuously becoming less interest-rate sensitive. Pull to par is the price-level companion to the maturity effect: discount bonds rise toward face value and premium bonds fall toward face value as maturity approaches. Zero-coupon bonds illustrate the maturity effect most cleanly, with duration equal to maturity at all times. Convexity also falls as maturity shortens, reducing the asymmetric price behaviour that benefits long-duration bondholders. Immunisation strategies require periodic rebalancing precisely because the maturity effect continuously erodes portfolio duration. For active fixed income managers, understanding how a bond’s risk profile changes over its life not just at purchase is essential to maintaining intended portfolio exposures.
The maturity effect is one of those concepts that seems almost too simple when you first encounter it. Of course a bond becomes less risky as it gets closer to maturing. But its implications ripple through fixed income portfolio management in ways that are anything but simple. Duration drift, pull to par, immunisation rebalancing, convexity decay all of these are the maturity effect showing up in different forms. Once you see it clearly, you start noticing it everywhere in how bond portfolios actually behave over time.
