The interest rate you get on gilts. Because the British Government is reckoned to be one of the least likely entities in the world to default on a loan, this rate of interest is reckoned to be about as close to risk-free as you can get. The equity risk premium is the average amount by which share returns are higher than gilt returns. In the UK this century, it has been about 5.6% per year and is effectively the bounty Fools get paid for taking the risk of investing in shares.