How do you calculate the Cost of Equity?

Cost of Equity = Risk-Free Rate + Beta * Equity Risk Premium

The risk-free rate represents how much a 10-year or 20-year US Treasury should yield; Beta is calculated based on the “riskiness” of Comparable Companies and the Equity Risk Premium is the % by which stocks are expected to out-perform “risk-less” assets.

Normally you pull the Equity Risk Premium from a publication called Ibbotson’s. 

Note: This formula does not tell the whole story. Depending on the bank and how precise you want to be, you could also add in a “size premium” and “industry premium” to account for how much a company is expected to out-perform its peers is according to its market cap or industry.

Small company stocks are expected to out-perform large company stocks and certain industries are expected to out-perform others, and these premiums reflect these expectations.