What is the Sharpe Ratio? Measuring Risk-Adjusted Returns

The Sharpe Ratio helps investors understand the return of an investment compared to its risk. It is the gold standard for evaluating fund performance.

The Sharpe Ratio is a metric used to calculate the excess return earned per unit of volatility in an investment asset or a trading strategy. Developed by William F. Sharpe in 1966, it is the most common way to compare the performance of hedge funds and portfolios. A higher Sharpe ratio indicates better risk-adjusted performance. A ratio of 1.0 is considered acceptable, 2.0 is very good, and 3.0 or higher is exceptional for institutional strategies.

The formula for the Sharpe Ratio is: $S_p = \frac{R_p - R_f}{\sigma_p}$. Here, $R_p$ is the return of the portfolio, $R_f$ is the risk-free rate, and $\sigma_p$ is the standard deviation of the portfolio's excess return. If a fund returns 12% in 2024 with a volatility of 10%, and the risk-free rate is 4%, the Sharpe Ratio is $(0.12 - 0.04) / 0.10 = 0.8$. This tells the investor if they are being compensated for taking on the additional volatility of the equity market compared to cash.

The Sharpe Ratio assumes that returns are normally distributed. It treats both 'upside' volatility (big gains) and 'downside' volatility (big losses) as equally bad because both increase the denominator $\sigma_p$. For strategies with asymmetric returns, such as selling deep out-of-the-money puts, the Sharpe Ratio can be artificially inflated. This led to the creation of the Sortino Ratio, which only considers downside deviation in its risk calculation.