Option-Adjusted Spread

The yield spread between a debt security with embedded options and the risk-free rate, adjusted to isolate the option's impact.

Option-Adjusted Spread (OAS) is a financial metric used to measure the yield difference between a bond with embedded options—such as callable corporate bonds or mortgage-backed securities—and a benchmark risk-free rate, typically represented by government Treasuries. Because embedded options can significantly alter a bond's cash flows depending on interest rate movements, a simple yield comparison is insufficient. The OAS calculation uses mathematical pricing models to simulate various interest rate paths, stripping away the value of the embedded option to isolate the "clean" spread. By removing the option's impact, the OAS isolates the compensation an investor receives for taking on the security's remaining risks, primarily credit risk and liquidity risk. This makes OAS the industry standard for comparing fixed-income securities with different structural features. For example, it allows an investor to directly compare a callable corporate bond with a non-callable corporate bond to see which offers better relative value. For investors, a widening OAS indicates that the security is becoming cheaper relative to Treasuries, offering more yield for its credit and liquidity risks. While this can lead to near-term capital losses as prices fall, it presents a higher-yielding entry point. Conversely, a narrowing OAS suggests the market is pricing in less risk, making the security more expensive. A common pitfall is relying solely on nominal spreads rather than OAS, which can lead investors to buy bonds with high yields that are actually poor values once the risk of the bond being called away is factored in.

A callable corporate bond has a nominal yield spread of 1.80% (180 basis points) over comparable Treasuries. An analyst uses a binomial pricing model to value the issuer's option to call the bond early, determining that this embedded call option is worth 0.65% (65 basis points) in yield. To find the clean credit and liquidity premium, the analyst subtracts the option value from the nominal spread: 1.80% - 0.65% = 1.15% (115 basis points). This 1.15% is the Option-Adjusted Spread.