Sortino Ratio Calculator
Measure risk-adjusted return using only downside deviation, so upside volatility is not penalised.
Quick answer: The Sortino ratio is a variant of the Sharpe ratio that divides excess return by downside deviation instead of total standard deviation. Because it ignores upside swings, it rewards strategies whose volatility is mostly to the good side. This tool subtracts the per-period risk-free rate from the mean, divides by the downside deviation, and annualises by the square root of periods per year.
How to use it
Enter the mean periodic return, the downside deviation (the standard deviation of only the returns that fell below the target, usually zero or the risk-free rate), the annual risk-free rate and periods per year. The output is the annualised Sortino ratio. As with Sharpe, the annual risk-free rate is divided by periods per year to match the return period.
Formula
Sortino = ( ( Mean − Risk-free ÷ Periods ) ÷ Downside deviation ) × √Periods
Downside deviation uses only returns below the target (typically zero), so favourable volatility does not inflate the denominator.
Limitations — what this calculator does not model
- Downside deviation is estimated from only the returns below the target, so it is unstable when losing periods are rare.
- The result depends on the chosen target (minimum acceptable return); a lenient target inflates the ratio.
- Like Sharpe, it reflects only the downside the data has shown and is blind to an unrealised tail loss.
- Uses the same simple annualisation assumptions and needs a reasonable sample to be meaningful.
Frequently asked questions
How does Sortino differ from Sharpe?
Sharpe divides by total standard deviation, which counts both up and down moves. Sortino divides only by downside deviation, so it does not punish a strategy for large gains. For the same data, Sortino is usually higher than Sharpe.
What is downside deviation?
It is the standard deviation computed from only the returns that fell below a target, commonly zero or the risk-free rate. Returns above the target are treated as zero deviation, so only harmful volatility is measured.
What target should a live system measure downside against?
Fix the target — the minimum acceptable return, usually zero or a short-dated risk-free rate — before monitoring, and apply it consistently across every strategy you compare. Because a lenient target flatters the ratio, the target must be stated in the ops dashboard for the number to mean anything.
Why can a live Sortino be unstable for a high-win-rate system?
Because downside deviation is estimated from only the subset of returns below the target, which can be a tiny sample when the system rarely loses. Adding one more losing period can then move the ratio noticeably, so treat short-run live Sortino with caution.
Does a high live Sortino mean the system is safe?
No. It only reflects the downside the data has actually shown, so a catastrophic loss the strategy has not yet suffered is invisible to it — exactly as with Sharpe. Pair it with a hard drawdown limit and tail-aware stress testing, not blind trust.
Why show both Sharpe and Sortino on an ops dashboard?
Because a Sortino much higher than Sharpe signals positively skewed returns, where much of the volatility is favourable upside that Sharpe penalises. Watching the two together tells you about the shape of the return distribution, not just its level.
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