Two funds both returned 12% last year. Which one is the better investment? The answer is not the one with the higher return โ it is the one that took less risk to get there. That is exactly what the Sharpe ratio measures.
What Is the Sharpe Ratio?
The Sharpe ratio, created by Nobel laureate William Sharpe, tells you how much return you earn per unit of risk you take. It is the single most widely used metric in portfolio analysis.
The Sharpe Ratio Formula
Sharpe Ratio = (Portfolio Return โ Risk-Free Rate) รท Portfolio Volatility
- Portfolio return โ your average annual return
- Risk-free rate โ what a safe asset pays (typically a 10-year treasury, ~3%)
- Volatility โ the standard deviation of your returns (how much they swing)
Worked Example
Fund A returns 12% with 10% volatility. Fund B returns 12% with 18% volatility. Risk-free rate is 3%.
| Fund | Return | Volatility | Sharpe Ratio |
|---|---|---|---|
| A | 12% | 10% | (12โ3) รท 10 = 0.90 |
| B | 12% | 18% | (12โ3) รท 18 = 0.50 |
Same return, but Fund A is clearly the better risk-adjusted investment.
How to Interpret Your Sharpe Ratio
| Sharpe Ratio | Quality |
|---|---|
| Above 3 | Excellent |
| 2 โ 3 | Very good |
| 1 โ 2 | Good |
| 0 โ 1 | Average โ barely paid for risk |
| Below 0 | Poor โ lost money after risk |
Common Mistakes
- Using total return instead of excess return โ always subtract the risk-free rate
- Comparing ratios over different time periods โ a 5-year Sharpe is not comparable to a 1-month Sharpe
- Ignoring that volatility punishes upside equally โ a fund that swings up 40% looks risky too
๐ก Pro Tip: When comparing two investments, the higher Sharpe ratio wins โ even if its headline return is lower. A 10% return with 5% volatility (Sharpe 1.4) beats a 14% return with 20% volatility (Sharpe 0.55).
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