The Sharpe ratio measures how much return a strategy earned for each unit of risk it took. Risk here means volatility - how much the returns bounced around. A high Sharpe ratio means smooth, efficient gains. A low one means you suffered a lot of turbulence for whatever profit you got.
The idea in plain terms
Profit alone does not tell you how hard a strategy was to hold. A curve that grinds steadily upward and a curve that lurches violently to the same endpoint feel completely different to trade. The Sharpe ratio captures that difference by dividing return by volatility, so a smoother path scores higher even at the same total return.
The formula
Sharpe ratio = (Average return - Risk-free rate) / Standard deviation of returns
- Average return - the mean return over the period, per trade or per time interval.
- Risk-free rate - what you could earn with no risk. Many retail traders set this to zero for simplicity.
- Standard deviation - how spread out the returns are. This is the "risk" or roughness term.
The bigger the numerator (return) and the smaller the denominator (volatility), the higher the Sharpe ratio.
Both strategies finished the year at the same balance. The smoother one is far easier to trade and far more likely to be traded correctly.
What counts as a good Sharpe ratio
- Below 1 - weak. The volatility is high for the return earned.
- Around 1 - acceptable for many strategies.
- 2 - very good; smooth, efficient returns.
- 3 or above - excellent, but on small samples treat it with suspicion.
These bands shift depending on how the ratio was calculated, so the safest use is comparative: rank your own strategies against each other using the same method.
Why traders care about it
A high-Sharpe strategy is easier to follow. Gentle drawdowns keep you calm, so you keep executing the plan. A low-Sharpe strategy with wild swings tends to break the trader before it breaks even - you bail out during a deep dip and miss the recovery. This is the same reason drawdown matters so much: the ride determines whether you can actually collect the edge.
Important: the Sharpe ratio treats big winning swings as "risk" too, because it only sees volatility, not direction. A strategy with occasional huge winners can be unfairly penalized. That is why you never judge a strategy on Sharpe alone.
The limits you must respect
- It penalizes upside volatility: large winners raise standard deviation and lower the ratio.
- It assumes normal-ish returns: trading returns often have fat tails it does not model well.
- It is sample-sensitive: a short backtest can produce a flattering figure that will not repeat.
Read the Sharpe ratio beside profit factor and expectancy. Together they describe efficiency, smoothness, and per-trade edge - a far more complete picture than any one metric.
Seeing it on your own strategies
You do not need to compute standard deviations by hand. When you backtest in a simulator, the session report calculates risk-adjusted metrics from your trade history, so you can compare a smooth strategy against a choppy one directly and pick the version you can actually hold through a bad month.
Sharpe ratio FAQ
What is a good Sharpe ratio for a trading strategy?
Roughly: below 1 is weak, around 1 is acceptable, 2 is very good, 3+ is excellent. Because the figure depends on how it is calculated, use it to compare your own strategies rather than as an absolute grade.
What does the Sharpe ratio actually measure?
Return per unit of volatility - how much reward a strategy produced for the roughness of its equity curve. Same profit with a smoother ride means a higher Sharpe ratio.
What are the limits of the Sharpe ratio?
It treats upside and downside volatility the same and assumes roughly normal returns, which trading often is not. Read it beside drawdown and profit factor.