Sharpe ratio

The Sharpe ratio is your average excess return divided by the standard deviation of your returns — return per unit of volatility. It answers a question that raw profit never does: how much bumpiness did you swallow to earn that number? A strategy returning 20% with wild swings can be strictly worse than one returning 12% smoothly, and the Sharpe ratio is how you see that. Higher is better; it means you're getting paid more for every unit of risk you take on.

How it's calculated

Take the mean of your period returns, subtract the risk-free rate (the return you could earn doing nothing risky), and divide by the standard deviation of those same returns.

Work it with daily numbers. Say your daily returns average 0.08%, the daily risk-free rate is roughly 0.02%, and the standard deviation of your daily returns is 0.9%. The per-day Sharpe is (0.08% − 0.02%) ÷ 0.9% = 0.067. That looks tiny, but you annualize it: 0.067 × √252 ≈ 0.067 × 15.87 ≈ 1.06. So on an annual basis you're earning just over one unit of return for each unit of volatility.

The risk-free rate matters more than beginners expect. When short-term rates sit near 5%, a strategy has to clear that bar before any of its return counts as skill — you could have parked the capital in T-bills and taken zero drawdown. Subtracting it keeps the ratio honest.

Why it matters

Return without a volatility context is a half-told story. Two accounts can both finish the year up 30%, but if one got there in a straight line and the other whipsawed through a 40% drawdown mid-year, they are not the same account. The second one is far more likely to blow up, far harder to hold through, and far more dependent on luck in the sequence of trades. The Sharpe ratio collapses that difference into a single comparable number.

Rough interpretation bands, annualized: below 1 is unremarkable, 1 to 2 is solid, 2 to 3 is very good, and above 3 is exceptional (and worth double-checking for a calculation error or overfit). Treat these as gut-check thresholds, not laws — a discretionary futures scalper and a long-only swing trader live in different regimes.

The ratio has one real flaw worth internalizing: it penalizes all volatility, including the upside kind. A month where you're suddenly up 15% raises your standard deviation and can drag your Sharpe down, even though nobody complains about violent profit. That's arguably backwards, since risk is really about the downside. The Sortino ratio addresses exactly this by dividing only by downside deviation — a useful companion metric when your return distribution is lopsided.

Related concepts

The Sharpe ratio is one lens; pair it with others so you're not fooled by a single summary statistic. Maximum drawdown tells you the worst peak-to-trough pain a smooth-looking Sharpe can still hide, and once you know that depth you can run the drawdown recovery calculator to see the return required to climb back out. Profit factor captures gross wins against gross losses without any volatility weighting, while trading expectancy tells you the average dollar outcome per trade — both of which can look healthy even when your Sharpe is mediocre because of erratic sizing.

To track your Sharpe ratio automatically across accounts and date ranges — with the risk-free rate and annualization handled for you — build it into your Tradeways dashboards and watch it move as your discipline does.