Duration management

A bond's price moves when interest rates move, and the size of that move depends on the bond's duration — the longer the duration, the bigger the swing. A debt fund manager who believes rates are about to change can use that fact on purpose.

If the manager expects rates to fall, bond prices should rise, and longer-duration bonds will rise more. So the manager lengthens the portfolio's duration, buying longer-maturity securities, to capture more of that gain.

If the manager expects rates to rise, the same logic runs backward: the manager shortens duration to limit the damage. This deliberate positioning is duration management, and it is a bet — if the rate view is wrong, the strategy loses instead of gains.

Chapter 10 describes duration management as a strategy adopted by funds with a mandate that permits it — a fund manager alters portfolio duration in anticipation of an interest rate scenario, increasing duration by moving into long-term maturities when rates are expected to fall, and the reverse when rates are expected to rise. The dynamic bond fund category is named specifically as one where the manager is free to take this view and position accordingly.

How much room a fund manager has depends entirely on the scheme's own mandate. An overnight fund must invest only in overnight securities, so there is no scope for duration management at all. An ultra-short-term debt fund has SEBI-defined maturity limits that constrain how far duration can move, though some room for an active call remains within that band. A money market or liquid fund, by contrast, earns purely on accrual — short maturities, low modified duration — precisely so there is no meaningful volatility from a wrong rate call.

Illustrative — the workbook describes the strategy without a worked duration-shift example.

A dynamic bond fund manager expects the RBI to cut rates over the next year. The scheme currently holds bonds with an average modified duration of 3 years. The manager shifts the portfolio toward longer-dated government securities, raising average modified duration to 6 years.

If yields subsequently fall by 0.50 percentage points across the curve, the approximate price gain is:

Price change ≈ −Modified duration × Change in yield
6 years case: −6 × (−0.50%) = +3.00%
3 years case (unchanged): −3 × (−0.50%) = +1.50%

On a Rs 1,000 crore portfolio, that is roughly Rs 15 crore more gain from lengthening duration than from leaving it unchanged. Had rates risen instead of fallen, the same 6-year portfolio would have lost about twice as much as the 3-year one.

Chapter 10 (Risk, Return and Performance of Funds) covers duration management alongside accrual strategies and credit-spread positioning, as part of how debt fund managers actively manage risk and return. Expect a question on which fund category (dynamic bond vs. overnight vs. ultra-short) has room for duration management, and on the direction of the duration call given a stated rate view.

• Longer duration when rates are expected to FALL, shorter duration when rates are expected to RISE — reversing this direction is the single most common error.
• Duration management is a bet, and the workbook is explicit that the risk is the view not materialising.
• Not every scheme category has room for this. Overnight and liquid funds are structurally excluded by their own mandate; dynamic bond funds are built for it.
• This is distinct from credit-spread positioning, a separate active strategy covered in the same section, which bets on rating migration rather than rate direction.