The Sortino ratio
Upside surprises are not a problem; losses are. The Sortino ratio measures return against only the volatility that hurts — the downside.
The Sortino ratio, explained.
The Sortino ratio is a risk-adjusted return measure that divides a strategy's excess return by its downside deviation — the volatility of negative returns only. It answers the same question as the Sharpe ratio, but counts only the risk that actually hurts.
The motivation is simple: standard deviation, which Sharpe uses, treats a +10% day and a −10% day as equally 'risky'. Most traders disagree — nobody complains about upside surprises. By measuring dispersion only below a target (usually zero), Sortino rewards strategies whose volatility is concentrated in their winners.
In practice the two ratios are read together. A strategy with a Sortino far above its Sharpe earns its volatility on the upside — think trend-following systems with small losses and occasional big runs. When the two are similar, the return stream is roughly symmetric. As with every backtest statistic, both describe one historical sample and degrade under overfitting.
From idea to a running bot.
The calculation differs from Sharpe in exactly one component.
Compute excess return
Start the same way as Sharpe: the strategy's return above a minimum acceptable baseline over the measurement period.
Measure downside deviation
Instead of the standard deviation of all returns, take the deviation of only the returns below the target. Positive periods contribute nothing to the risk term.
Divide and compare
Excess return over downside deviation gives the ratio. Compare it against the same strategy's Sharpe: a big gap means the volatility is mostly upside.
Built for the way you trade.
Sortino is most useful where return streams are asymmetric.
Trend and breakout traders
Strategies designed to lose small and win big are systematically undersold by Sharpe. Sortino gives their asymmetry fair credit.
Strategy comparers
Ranking backtests by Sortino instead of raw return filters out strategies that got their profits through terrifying downside swings.
VolatiCloud backtesters
VolatiCloud backtest reports include Sortino next to Sharpe, Calmar, and drawdown, so the asymmetry check is one glance, not a spreadsheet.
- Excess return divided by downside deviation
- Ignores upside volatility — only losses count as risk
- Higher than Sharpe ⇒ volatility concentrated in winners
- Best read alongside Sharpe and maximum drawdown
- Reported in every VolatiCloud backtest
Frequently asked questions.
What is a good Sortino ratio?
Benchmarks mirror Sharpe's, shifted up slightly since the denominator is smaller: below 1 is weak, 1-2 is decent, above 2 is strong. Extremely high backtest values usually indicate overfitting rather than a miracle strategy.
When should I prefer Sortino over Sharpe?
When the strategy's returns are asymmetric — big winners, small losers, or the reverse. Sharpe punishes both tails equally; Sortino isolates the harmful one. For roughly symmetric strategies the two tell the same story.
Why does my strategy's Sortino differ so much from its Sharpe?
A Sortino well above Sharpe means most of the volatility came from gains, which standard deviation counted as risk but downside deviation ignored. A Sortino close to or below Sharpe suggests the losses drive the volatility.
Where do I see Sortino on VolatiCloud?
In the backtest results for any strategy, alongside Sharpe, Calmar, maximum drawdown, profit factor, and expectancy — computed from the same simulated trades on real historical data.
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