Direct Answer
A bond's yield minus the interpolated swap rate of the same maturity. It measures the bond's extra yield over the interest rate swap curve instead of the government curve. A wider I-spread means more yield over the swap curve, a benchmark that reflects bank funding conditions.
I-Spread: Formula, Meaning, Signals, Examples and How to Use It
How Is I-Spread Calculated?
A bond's yield minus the interpolated swap rate of the same maturity. It measures the bond's extra yield over the interest rate swap curve instead of the government curve.
Formula: I-spread (bp) = (bond yield - interpolated swap rate at the bond's maturity) x 100
Inputs:
- Bond yield (percent)
- Swap rates bracketing the bond's maturity
- Same observation date and compounding basis
Worked example. A bond yielding 5.40% against an interpolated swap rate of 4.55% has an I-spread of 85 basis points. The inputs are illustrative numbers, not market data.
Reading it. A wider I-spread means more yield over the swap curve, a benchmark that reflects bank funding conditions. It is often used for corporate and financial bonds that trade relative to swaps.
Limits. Swap and bond yields must use the same compounding and day-count basis, and swap spreads to government bonds can shift, which changes the I-spread even when the government G-spread stays the same.
What is I-Spread?
A bond's yield minus the interpolated swap rate of the same maturity. It measures the bond's extra yield over the interest rate swap curve instead of the government curve.
How to use I-Spread
A wider I-spread means more yield over the swap curve, a benchmark that reflects bank funding conditions. It is often used for corporate and financial bonds that trade relative to swaps. A reading alone is never a buy or sell signal; it needs context from price structure, volume, volatility and the broader market regime.
Strengths
- Using the swap curve as the reference gives a benchmark that is not tied to one government's issuance or supply swings.
- Swap quotes cover regular annual tenors, so the matching benchmark point is usually observed rather than estimated.
- Reproducible when the formula and data convention are fixed.
Weaknesses and limitations
- Because swap rates embed bank credit and funding terms, the benchmark itself carries risk that a government curve does not.
- It is quoted off a fixed-rate swap, so a floating-coupon bond or one with an irregular schedule is not matched to the reference without conversion.
- Correlated indicators can create false confidence by repeating the same underlying information.
Editorial and risk note
This page is educational content, not individualized investment advice. It should not imply guaranteed prediction, accuracy or outperformance.
Frequently Asked Questions
Is I-Spread a buy or sell signal?
No. A wider I-spread means more yield over the swap curve, a benchmark that reflects bank funding conditions. Swap and bond yields must use the same compounding and day-count basis, and swap spreads to government bonds can shift, which changes the I-spread even when the government G-spread stays the same. A trade built on it still needs a trigger, an invalidation rule, a position size and realistic execution assumptions.
What is the best setting for I-Spread?
I-Spread is computed from bond yield (percent); swap rates bracketing the bond's maturity; same observation date and compounding basis, so the choices that matter are the data convention and the window it is read over. Test those across instruments, regimes and out-of-sample periods instead of fitting one historical winner.
Can I-Spread be used by itself?
Swap and bond yields must use the same compounding and day-count basis, and swap spreads to government bonds can shift, which changes the I-spread even when the government G-spread stays the same. For that reason it is read next to measures of direction, participation, valuation, liquidity and risk, not alone.
Does I-Spread work on every timeframe?
The calculation (I-spread (bp) = (bond yield - interpolated swap rate at the bond's maturity) x 100) can be run on any bar size, but behavior is not portable: a reading on a five-minute chart describes a very different market window from the same reading on a daily chart. Validate the exact timeframe before relying on it.
Why does I-Spread give false signals?
Because swap rates embed bank credit and funding terms, the benchmark itself carries risk that a government curve does not. It is quoted off a fixed-rate swap, so a floating-coupon bond or one with an irregular schedule is not matched to the reference without conversion. Lag, noise and regime changes add to this, because market participants react to new information after the reading is calculated.
How should I-Spread be backtested?
Rebuild I-Spread from bond yield (percent) using point-in-time data, write the rules before testing, include delisted securities where relevant, model realistic fills and costs, reserve a validation sample and compare with a simpler baseline.