Callable Bond Valuation with Credit Curves and OAS

Summary

The document asks how an issuer can value a callable bond before knowing its option-adjusted spread. It explains the market practice described in the answer: construct a credit curve from noncallable bonds when possible, then use an interest-rate lattice or Monte Carlo model with volatility inputs from interest-rate derivatives. The model’s callable-bond value can then be compared with its market price, with OAS serving as the implied spread that reconciles them.

The answer cautions that this approach may not reproduce market prices well. More elaborate models represent the credit process explicitly and model how it interacts with the call option. It also notes that traders often work with a market-implied OAS without treating it as a direct measure of the spread on noncallable credit. The discussion offers a practical framing rather than a worked valuation, model specification, or evidence comparing methods; it does not resolve how an issuer should determine fair value independently of market conventions.

Key ideas

• A credit curve from noncallable issues can provide a starting point for callable-bond valuation.
• Interest-rate lattices or Monte Carlo simulations can incorporate rates and volatility when valuing the call feature.
• The option-adjusted spread is treated as the implied spread that aligns model value with the observed callable-bond price.
• A basic credit-curve approach may fit market prices poorly because credit risk and the call option interact.
• More explicit models can represent both the credit process and its interaction with the embedded option.

Tags

# Pricing a callable bond


# Pricing a callable bond












I have read the Lehman Brother's paper on OAS which I mostly understand, they outline how to find the OAS for a callable bond of which the formula is effectively (ignoring refinancing costs):

Market Price Callable = Value of Stripped Bond - Value of Option

They proceed to simulate a number of interest rate paths using zero coupon interest rates from the treasury curve and then pricing the stripped bond and the option they arrive at a price which is too high, thus we need to add the OAS spread in order to discount the price to the market price of the callable. The spread value that achieves this is the OAS.

My question therefore is, how do you price the callable bond in the first place if I was the issuer before having the OAS, I think my confusion is that the calculated price in this case is too high and therefore adding the OAS discounts further to equal the market price but if we don't know the OAS surely calculating the price of the stripped bond minus the price of the option will not equal that of the market price.

## Answer by zpablo24 (score 1)

https://quant.stackexchange.com/a/45182

A common approach is to build a credit curve from noncallable issues if available, and then run your lattice or monte carlo on that using volatilities from interest rate derivatives market possibly adjusted. I have heard however that that approach doesnt do a great job hitting market prices, and there are more complex models which involve more explicit representation of the credit process and its interaction with the call option. Seems like most traders just accept that there is a market implied OAS, and dont worry so much about how it relates to noncallable credit spreads.

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This summary was written by Stratmill's research agent from the original; it is not a copy of the source.