The Sharpe ratio measures an investment's excess return (over the risk-free rate) divided by its volatility. The higher it is, the better the return compensates for the risk taken — a ratio above 1 is generally considered good.
How do you calculate the Sharpe ratio?
The formula is straightforward:
Sharpe = (Portfolio return − Risk-free rate) / Standard deviation of returns
The risk-free rate benchmark is usually short-term government bonds (3-month T-Bills in the US, 3-month OAT in France). Standard deviation measures the dispersion of returns: the more irregular the performance, the higher it is, and the more it penalizes the final ratio.
Example: a portfolio returns 12% per year with 15% volatility, risk-free rate at 3%. Sharpe = (12 − 3) / 15 = 0.60.
What counts as a good Sharpe ratio?
| Sharpe Ratio | Interpretation |
|---|---|
| < 0 | Return below the risk-free rate — poor |
| 0 - 0.5 | Weak compensation for risk taken |
| 0.5 - 1 | Decent, in line with market average |
| 1 - 2 | Good, solid risk-adjusted return |
| > 2 | Excellent (rare over the long run) |
As a reference point, the S&P 500 has historically shown a Sharpe ratio around 0.4 to 0.6 over the long term, with significant variation depending on the market cycle.
Why isn't the Sharpe ratio enough on its own?
Two limitations are well known. First, it treats upside and downside volatility the same way: a stock that climbs strongly but erratically is penalized just as much as one that falls erratically, even though the impact isn't the same for the investor. This is why the Sortino ratio, which only penalizes downside volatility, is sometimes preferred.
Second, the Sharpe ratio assumes a normal distribution of returns, which isn't always true in practice: crashes and fatter tail distributions are underestimated.
How do you compare two portfolios using the Sharpe ratio?
It's most useful in relative comparisons: between two funds, two strategies, or a portfolio versus its benchmark index. A portfolio with a lower gross return but a higher Sharpe ratio may represent a more efficient investment, since it achieves its performance with fewer bumps along the way. This is why it's risky to judge a portfolio on its displayed return alone: two portfolios both up 15% per year can have radically different risk profiles.
How to use this in practice?
The Sharpe ratio is one of the indicators calculated during InvestIQ's free portfolio audit: it helps position a real portfolio's risk-adjusted performance against a benchmark index, alongside diversification and the financial soundness of positions (measured for instance via the Piotroski F-Score). It's never a standalone number — it only makes sense in context, tracked over time or compared to a benchmark, much like the InvestIQ Score combines several dimensions (momentum, quality, valuation) rather than relying on a single indicator.
This is not investment advice.
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Frequently asked questions
A ratio above 1 is considered good, between 0.5 and 1 is decent, and below 0.5 the compensation for risk is weak. Above 2, performance is excellent but rare over the long term.
The Sharpe ratio penalizes all volatility, both positive and negative. The Sortino ratio only accounts for downside volatility, making it more representative of the risk investors actually perceive.
Yes, when the portfolio's return is below the risk-free rate. This means the investor would have gotten a better risk-adjusted result by putting their money in a risk-free asset instead.
