Floating Rate and Inflation Indexed Bonds: Structure and Valuation (IIBF TIRM)

In IIBF's Treasury Investment and Risk Management (TIRM) paper, floating rate and inflation indexed bonds are two of the most misread instrument classes because their cash flows do not behave like a plain-vanilla fixed-coupon bond. A floating rate bond resets its coupon periodically off a benchmark plus a fixed spread, which is why its price barely moves even when market rates swing. An inflation indexed bond goes a step further and adjusts the principal itself to a price index, so both the coupon and the redemption amount track inflation. This article walks through the reset mechanism, the duration behaviour, the real-versus-nominal yield framework, and how a bank treasury actually deploys each instrument — exactly the way TIRM exam questions test it.

📊 Floating Rate Bonds: The Coupon Reset Mechanism

A floating rate bond (FRB) pays a coupon defined as a benchmark rate plus a fixed spread. The spread is discovered once, at issuance — through auction or negotiated pricing — and stays constant for the life of the bond. The benchmark component, by contrast, is refixed on every reset date, so the coupon amount itself changes across the bond's life even though the spread never does.

Two mechanical details matter for the exam. First, the reset date is the point at which the next coupon is fixed; it does not have to coincide with the coupon payment date, though the two are usually close together. Second, the reference period is the window over which the benchmark is observed — often an average taken over a short run of days before the reset date rather than a single day's print — precisely to prevent the coupon from being anchored to one noisy or manipulable observation.

Once the reset happens, the new coupon applies for the following coupon period only, and the process repeats at the next reset date. This is conceptually different from the money market instruments a treasury uses to fund itself, and also different from a bond built through the STRIPS in government securities process, where every future cash flow is stripped out and fixed in advance. An FRB's cash flows are never fixed in advance beyond the current reset period — that is the entire point of the structure.

💹 Why the Price Stays Near Par: Interest Rate Duration vs Spread Duration

Because the coupon realigns with the market benchmark at every reset, an FRB's interest-rate duration is not measured to maturity — it is measured to the next reset date. A bond maturing in eight years but resetting every quarter behaves, for interest-rate risk purposes, like a three-month instrument: once the coupon is refixed to the prevailing rate, the bond is again priced fairly for the new coupon it will pay, so its price snaps back close to par at each reset. This is why FRB prices are far less volatile than fixed-coupon bonds of the same maturity when the general level of interest rates moves.

The spread, however, tells a different story. It was locked in at issuance and does not reset with the benchmark. If the market's required spread for that issuer or instrument category widens — because credit perception changes, liquidity dries up, or supply increases — the bond's price does move, even though the benchmark component of the coupon is behaving perfectly. This sensitivity is captured by spread duration, and unlike interest-rate duration, spread duration runs all the way to the bond's final maturity, not just to the next reset date.

💡 Exam Tip: If a question asks you to compute the interest-rate risk of an FRB, use the time to the next reset date, not the time to maturity. If it asks about credit-spread risk on the same bond, switch to spread duration and use the full residual maturity instead.

Treasury desks exploit this split deliberately: FRBs let them take a spread view on an issuer while staying largely neutral to the direction of general interest rates, which is a very different risk profile from holding a plain fixed-rate bond of the same tenor.

📈 Inflation Indexed Bonds: Indexed Principal, Real Yield and Breakeven

An inflation indexed bond (IIB) works on an entirely different mechanic. Instead of resetting the coupon rate, it resets the principal. The face value is periodically adjusted to a price index, producing an "indexed principal" that rises (or falls) as the index moves. The coupon rate itself is fixed at issuance as a real rate, but it is applied to the indexed principal rather than to the original face value — so the actual rupee coupon paid out changes every period even though the percentage rate never does.

This is the source of the real-versus-nominal yield distinction that TIRM candidates must be comfortable with. The real yield is what the IIB delivers after inflation is stripped out — it is effectively the return on purchasing power. The nominal yield is what a comparable plain fixed-coupon government bond of similar maturity offers, with no adjustment for inflation. Neither number alone tells you which bond an investor should prefer; the comparison needs a bridge.

That bridge is the breakeven inflation rate: the nominal yield on a comparable fixed-rate bond minus the real yield on the IIB of matching maturity. It is the inflation rate at which an investor would be exactly indifferent between the two instruments. If realised inflation over the holding period turns out higher than the breakeven, the IIB delivers the better outcome; if realised inflation comes in lower, the fixed-rate bond wins. Treasury desks read the breakeven off market prices as a running, market-implied inflation forecast, which is one reason IIB pricing is watched even by desks that hold none.

📌 Remember: Breakeven inflation = nominal yield of a comparable fixed-rate bond minus the real yield of the inflation indexed bond. It is a forecast extracted from prices, not a guaranteed outcome.

🛡️ Deflation Protection, Taxation, Accounting and Treasury Use

If the price index falls over an IIB's life — a deflationary spell — the indexed principal can drop below the bond's original face value. A properly designed IIB carries a deflation floor: the amount actually paid out at redemption is never less than the original face value, even if the indexed principal computed along the way had fallen short of it. That protection applies specifically to the redemption payment, not to every coupon date in between.

⚠️ Common Mistake: Candidates often assume the deflation floor protects every coupon payment. It does not — coupons continue to be computed on the indexed principal as it stands at each date, including a lower figure during a deflationary period. Only the final redemption amount is floored at par.

On taxation and accounting, treat both instruments with the same discipline you would any other bank investment. Coupon income on FRBs and IIBs is taxable in the year it is received under the applicable income-tax provisions, and for IIBs the periodic increase in the indexed principal also attracts the tax treatment prescribed for such instruments — it is not automatically a tax-free capital gain, and candidates should not assume otherwise. For banks, both instruments sit in the investment book and are classified and valued under the RBI's investment classification framework, with FRBs marked using the benchmark-plus-spread curve and IIBs valued with reference to the prevailing indexed principal. You can review the underlying valuation and classification rules on the Reserve Bank of India website.

In practice, a bank treasury uses these two instruments for very different jobs. FRBs shrink the duration gap on a balance sheet funded largely by rate-sensitive liabilities, or park surplus liquidity without taking on large mark-to-market risk if rates rise — exactly the kind of exposure covered under Risk Analysis and Control. IIBs, by contrast, hedge the real value of long-duration, inflation-linked obligations and diversify the portfolio's risk factors beyond plain nominal-rate risk. Both positions are still run within the treasury risk limits and exposure ceilings the investment policy lays down, the same discipline that governs how a bank uses currency swaps for corporate hedging on the client side of the book.

🧠 Practice MCQs: Floating Rate and Inflation Indexed Bonds

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🎯 Study These Instruments the Way TIRM Tests Them

Floating rate and inflation indexed bonds are two of the clearest examples in TIRM of why treasury professionals cannot rely on plain fixed-coupon bond intuition. Once you separate the resetting element (coupon on an FRB, principal on an IIB) from the fixed element (spread on an FRB, real rate on an IIB), the duration behaviour, the real-versus-nominal yield framework, and the deflation floor all follow logically. Revisit the Capital Market chapter alongside the sibling notes on the government securities auction process and the Fully Accessible Route for government securities to see how these instruments are issued and traded before they reach a treasury book. For the complete set of TIRM notes, browse the Treasury Investment and Risk Management tag, then lock in the concepts with a timed test on iibf.store's CAIIB course.