Arbitrage pricing theory (APT) is a multi-factor asset pricing model based on the idea that an asset's returns can be predicted using the linear relationship between the asset's expected return and a number of macroeconomic variables that capture systematic risk.

The arbitrage pricing theory is an alternative to the CAPM that uses fewer assumptions and can be harder to implement than the CAPM. While both are useful, many investors prefer to use the CAPM, a one-factor model, over the more complicated APT, which requires users to quantify multiple factors.

Definition. The Capital Asset Pricing Model (CAPM) and the Arbitrage Pricing theory (APT) are models used to theoretically determine the rate of return on a portfolio. While the CAPM assumes the direct relationship between assets, APT assumes a linear connection between risk factors.

As such, APT argues that when opportunities for arbitrage are exhausted in a given period, then the expected return of an asset is a linear function of various factors or theoretical market indices, where sensitivities of each factor is represented by a factor-specific beta coefficient or factor loading.