Hong Life CalculatorsUnderstanding the Sharpe ratio calculator — concept and principle
The Sharpe ratio measures how much extra return an investment earned for each unit of risk it took. It lets you compare funds or portfolios with different returns and volatility on one scale. This calculator takes the annual return, the risk-free rate and the annual volatility (standard deviation of returns) and returns the Sharpe ratio with a simple rating.
How it is calculated
- Excess return = portfolio return − risk-free rate.
- Sharpe ratio = excess return ÷ standard deviation of returns.
All three inputs should be annual percentages over the same period. The risk-free rate is usually a short-term government bill yield. The calculator labels results of 1 or more as good, 0.5 to 1 as acceptable and below 0.5 as weak, which are common rules of thumb rather than a formal standard.
The principle
William F. Sharpe proposed the ratio in 1966 as a "reward-to-variability" measure. Anyone can earn the risk-free rate without taking risk, so only the return above it is a reward for bearing risk. Dividing by volatility puts risky and less risky portfolios on the same footing: a portfolio with a 12% return and 20% volatility may be less efficient than one with 8% and 8%. In theory, combining the highest-Sharpe portfolio with cash or leverage can achieve any risk level with the best available reward.
Worked example
Default inputs: return 10%, risk-free rate 4%, volatility 15%.
- Excess return: 10% − 4% = 6%.
- Sharpe ratio: 6 ÷ 15 = 0.40.
- Rating: below 0.5, so weak.
How to read the result
A higher Sharpe ratio means more return per unit of risk. Broad stock markets have historically had long-run Sharpe ratios of roughly 0.3–0.5, so values persistently above 1 are uncommon for diversified portfolios and deserve scrutiny. Compare only ratios computed over the same period and with the same return frequency, and annualise consistently.
Common mistakes
- Mixing monthly volatility with annual returns.
- Using a short, unusually calm period that understates risk.
- Comparing ratios across different time windows.
- Ignoring that volatility treats upside and downside swings alike.
Frequently asked questions
What is a good Sharpe ratio?
Above 1 is often called good for a diversified portfolio, but compare with peers and the market over the same period.
Can the Sharpe ratio be negative?
Yes, when the return is below the risk-free rate.
How is it different from the Sortino ratio?
Sortino divides by downside deviation only, so upside volatility is not penalised.
Sources: Sharpe, W. F., "Mutual Fund Performance", Journal of Business (1966) · Sharpe, W. F., "The Sharpe Ratio", Journal of Portfolio Management (1994)