Option-adjusted spread (OAS) is the yield spread which has to be added to a benchmark yield curve to discount a security's payments to match its market price, using a dynamic pricing model that accounts for embedded options. OAS is hence model-dependent. This concept can be applied to a mortgage-backed security (MBS), or another bond with embedded options, or any other interest rate derivative or option. More loosely, the OAS of a security can be interpreted as its "expected outperformance" versus the benchmarks, if the cash flows and the yield curve behave consistently with the valuation model.
In the context of an MBS or callable bond, the embedded option relates primarily to the borrower's right to early repayment, a right commonly exercised via the borrower refinancing the debt. These securities must therefore pay higher yields than noncallable debt, and their values are more fairly compared by OAS than by yield. OAS is usually measured in basis points (bp, or 0.01%).
For a security whose cash flows are independent of future interest rates, OAS is essentially the same as Z-spread.
In contrast to simpler "yield-curve spread" measurements of bond premium using a fixed cash-flow model (I-spread or Z-spread), the OAS quantifies the yield premium using a probabilistic model that incorporates two types of volatility:
Designing such models in the first place is complicated because prepayment rates are a path-dependent and behavioural function of the stochastic interest rate. (They tend to go up as interest rates come down.) Specially calibrated Monte Carlo techniques are generally used to simulate hundreds of yield-curve scenarios for the calculation.
OAS is an emerging term with fluid use across MBS finance. The definition here is based on Lakhbir Hayre's Mortgage-Backed Securities textbook. Other definitions are rough analogs:
Treasury bonds (or alternate benchmarks, such as the noncallable bonds of some other borrower, or interest rate swaps) are generally not available with maturities exactly matching MBS cash flow payments, so interpolations are necessary to make the OAS calculation.
For an MBS, the word "option" in option-adjusted spread relates primarily to the right of property owners, whose mortgages back the security, to prepay the mortgage amount. Since mortgage borrowers will tend to exercise this right when it is favourable for them and unfavourable for the bond-holder, buying an MBS implicitly involves selling an option. (The presence of interest-rate caps can create further optionality.) The embedded "option cost" can be quantified by subtracting the OAS from the Z-spread (which ignores optionality and volatility).
Since prepayments typically rise as interest rates fall and vice versa, the basic (pass-through) MBS typically has negative bond convexity (second derivative of price over yield), meaning that the price has more downside than upside as interest rates vary. The MBS-holder's exposure to borrower prepayment has several names:
This difference in convexity can also be used to explain the price differential from an MBS to a Treasury bond. However, the OAS figure is usually preferred. The discussion of the "negative convexity" and "option cost" of a bond is essentially a discussion of a single MBS feature (rate-dependent cash flows) measured in different ways.
Fixed income refers to any type of investment under which the borrower or issuer is obliged to make payments of a fixed amount on a fixed schedule. For example, the borrower may have to pay interest at a fixed rate once a year and repay the principal amount on maturity. Fixed-income securities can be contrasted with equity securities that create no obligation to pay dividends or any other form of income. Bonds carry a level of legal protections for investors that equity securities do not: in the event of a bankruptcy, bond holders would be repaid after liquidation of assets, whereas shareholders with stock often receive nothing.
Bond valuation is the process by which an investor arrives at an estimate of the theoretical fair value, or intrinsic worth, of a bond. As with any security or capital investment, the theoretical fair value of a bond is the present value of the stream of cash flows it is expected to generate. Hence, the value of a bond is obtained by discounting the bond's expected cash flows to the present using an appropriate discount rate.
In finance, the duration of a financial asset that consists of fixed cash flows, such as a bond, is the weighted average of the times until those fixed cash flows are received. When the price of an asset is considered as a function of yield, duration also measures the price sensitivity to yield, the rate of change of price with respect to yield, or the percentage change in price for a parallel shift in yields.
In finance, bond convexity is a measure of the non-linear relationship of bond prices to changes in interest rates, and is defined as the second derivative of the price of the bond with respect to interest rates. In general, the higher the duration, the more sensitive the bond price is to the change in interest rates. Bond convexity is one of the most basic and widely used forms of convexity in finance. Convexity was based on the work of Hon-Fei Lai and popularized by Stanley Diller.
A collateralized mortgage obligation (CMO) is a type of complex debt security that repackages and directs the payments of principal and interest from a collateral pool to different types and maturities of securities, thereby meeting investor needs.
A mortgage-backed security (MBS) is a type of asset-backed security which is secured by a mortgage or collection of mortgages. The mortgages are aggregated and sold to a group of individuals that securitizes, or packages, the loans together into a security that investors can buy. Bonds securitizing mortgages are usually treated as a separate class, termed residential; another class is commercial, depending on whether the underlying asset is mortgages owned by borrowers or assets for commercial purposes ranging from office space to multi-dwelling buildings.
A corporate bond is a bond issued by a corporation in order to raise financing for a variety of reasons such as to ongoing operations, mergers & acquisitions, or to expand business. It is a longer-term debt instrument indicating that a corporation has borrowed a certain amount of money and promises to repay it in the future under specific terms. Corporate debt instruments with maturity shorter than one year are referred to as commercial paper.
Fixed-income arbitrage is a group of market-neutral-investment strategies that are designed to take advantage of differences in interest rates between varying fixed-income securities or contracts. Arbitrage in terms of investment strategy, involves buying securities on one market for immediate resale on another market in order to profit from a price discrepancy.
Fixed income analysis is the process of determining the value of a debt security based on an assessment of its risk profile, which can include interest rate risk, risk of the issuer failing to repay the debt, market supply and demand for the security, call provisions and macroeconomic considerations affecting its value in the future. Based on such an analysis, a fixed income analyst tries to reach a conclusion as to whether to buy, sell, hold, hedge or avoid the particular security.
Prepayment is the early repayment of a loan by a borrower, in part or in full, often as a result of optional refinancing to take advantage of lower interest rates.
In finance, the yield spread or credit spread is the difference between the quoted rates of return on two different investments, usually of different credit qualities but similar maturities. It is often an indication of the risk premium for one investment product over another. The phrase is a compound of yield and spread.
Commercial mortgage-backed securities (CMBS) are a type of mortgage-backed security backed by commercial and multifamily mortgages rather than residential real estate. CMBS tend to be more complex and volatile than residential mortgage-backed securities due to the unique nature of the underlying property assets.
Reinvestment risk is a form of financial risk. It is primarily associated with fixed income securities, in the form of early redemption risk and coupon reinvestment risk.
In finance, a lattice model is a technique applied to the valuation of derivatives, where a discrete time model is required. For equity options, a typical example would be pricing an American option, where a decision as to option exercise is required at "all" times before and including maturity. A continuous model, on the other hand, such as Black–Scholes, would only allow for the valuation of European options, where exercise is on the option's maturity date. For interest rate derivatives lattices are additionally useful in that they address many of the issues encountered with continuous models, such as pull to par. The method is also used for valuing certain exotic options, where because of path dependence in the payoff, Monte Carlo methods for option pricing fail to account for optimal decisions to terminate the derivative by early exercise, though methods now exist for solving this problem.
The Z-spread, ZSPRD, zero-volatility spread, or yield curve spread of a bond is the parallel shift or spread over the zero-coupon Treasury yield curve required for discounting a predetermined cash flow schedule to arrive at its present market price. The Z-spread is also widely used in the credit default swap (CDS) market as a measure of credit spread that is relatively insensitive to the particulars of specific corporate or government bonds.
The following outline is provided as an overview of and topical guide to finance:
Fixed-income attribution is the process of measuring returns generated by various sources of risk in a fixed income portfolio, particularly when multiple sources of return are active at the same time.
A renewable energy derivative is based on a new method of securitization, which is a structured finance process that pools and repackages cash-flow-producing financial assets into securities which are then sold to investors. The term "securitization" is derived from the fact that securities are used to obtain funds from investors.
Securitization is the financial practice of pooling various types of contractual debt such as residential mortgages, commercial mortgages, auto loans or credit card debt obligations and selling their related cash flows to third party investors as securities, which may be described as bonds, pass-through securities, or collateralized debt obligations (CDOs). Investors are repaid from the principal and interest cash flows collected from the underlying debt and redistributed through the capital structure of the new financing. Securities backed by mortgage receivables are called mortgage-backed securities (MBS), while those backed by other types of receivables are asset-backed securities (ABS).
In mathematical finance, convexity refers to non-linearities in a financial model. In other words, if the price of an underlying variable changes, the price of an output does not change linearly, but depends on the second derivative of the modeling function. Geometrically, the model is no longer flat but curved, and the degree of curvature is called the convexity.