Direct Answer
The constant spread added to the benchmark curve (across simulated interest-rate paths) that makes a bond's model price equal its market price, after accounting for embedded options such as calls or prepayments. OAS is the spread for credit and liquidity risk once option effects are stripped out, so it allows comparing bonds with and without options. OAS depends on the interest-rate model and volatility input, so it is a model output rather than an observed quantity.
Option-Adjusted Spread: Formula, Meaning, Signals, Examples and How to Use It
How Is Option-Adjusted Spread Calculated?
The constant spread added to the benchmark curve (across simulated interest-rate paths) that makes a bond's model price equal its market price, after accounting for embedded options such as calls or prepayments.
Formula: Find s so that Price = average over rate paths of PV(cash flows discounted at path rates + s). OAS approx = Z-spread - option cost
Inputs:
- Market price
- Benchmark curve and volatility assumption
- Option terms (call schedule or prepayment model)
Worked example. A callable bond with a Z-spread of 140 bp and an option cost of 35 bp has an OAS of about 105 basis points. The inputs are illustrative numbers, not market data.
Reading it. OAS is the spread for credit and liquidity risk once option effects are stripped out, so it allows comparing bonds with and without options. A higher OAS means more compensation for the same modeled option.
Limits. OAS depends on the interest-rate model and volatility input, so it is a model output rather than an observed quantity. Different vendors can report different OAS for the same bond.
What is Option-Adjusted Spread?
The constant spread added to the benchmark curve (across simulated interest-rate paths) that makes a bond's model price equal its market price, after accounting for embedded options such as calls or prepayments.
How to use Option-Adjusted Spread
OAS is the spread for credit and liquidity risk once option effects are stripped out, so it allows comparing bonds with and without options. A higher OAS means more compensation for the same modeled option. A reading alone is never a buy or sell signal; it needs context from price structure, volume, volatility and the broader market regime.
Strengths
- One spread number summarizes the extra yield after valuing the call or prepayment option, so callable and non-callable bonds can be compared.
- Averaging across simulated paths means the figure reflects option value in many rate scenarios, not only along today's single forward curve.
- Reproducible when the formula and data convention are fixed.
Weaknesses and limitations
- The market price enters as a given, so a stale or indicative price for an illiquid bond flows straight into the spread.
- Raising the volatility input increases the value attributed to the issuer's call option, which lowers a callable bond's OAS for an unchanged price.
- 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 Option-Adjusted Spread a buy or sell signal?
No. OAS is the spread for credit and liquidity risk once option effects are stripped out, so it allows comparing bonds with and without options. OAS depends on the interest-rate model and volatility input, so it is a model output rather than an observed quantity. 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 Option-Adjusted Spread?
Option-Adjusted Spread is computed from market price; benchmark curve and volatility assumption; option terms (call schedule or prepayment model), 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 Option-Adjusted Spread be used by itself?
OAS depends on the interest-rate model and volatility input, so it is a model output rather than an observed quantity. Different vendors can report different OAS for the same bond. For that reason it is read next to measures of direction, participation, valuation, liquidity and risk, not alone.
Does Option-Adjusted Spread work on every timeframe?
The calculation (Find s so that Price = average over rate paths of PV(cash flows discounted at path rates + s). OAS approx = Z-spread - option cost) 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 Option-Adjusted Spread give false signals?
The market price enters as a given, so a stale or indicative price for an illiquid bond flows straight into the spread. Raising the volatility input increases the value attributed to the issuer's call option, which lowers a callable bond's OAS for an unchanged price. Lag, noise and regime changes add to this, because market participants react to new information after the reading is calculated.
How should Option-Adjusted Spread be backtested?
Rebuild Option-Adjusted Spread from market price 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.