The Sortino ratio is a modification of the Sharpe ratio that distinguishes between harmful volatility and total volatility. Developed by Frank A. Sortino, it replaces standard deviation in the denominator with downside deviation, focusing exclusively on returns that fall below a minimum acceptable return threshold. This makes the Sortino ratio a more accurate measure of risk-adjusted performance for strategies where upside volatility is desirable.
The formula
Sortino Ratio = (Rp - MAR) / Downside Deviation
Where Rp is the portfolio return, MAR is the minimum acceptable return (often set to the risk-free rate or zero), and downside deviation is the standard deviation calculated using only negative excess returns. Returns above the MAR are excluded from the volatility calculation entirely.
Why the Sortino ratio matters
The fundamental insight behind the Sortino ratio is that investors care about losses more than gains. A strategy that generates a 15% return with frequent large upside swings is very different from one that generates 15% with frequent large drawdowns, yet both might have similar Sharpe ratios because standard deviation treats upside and downside volatility identically.
Consider a trend-following strategy that produces many small losses (from false signals) but occasionally captures large trends. The standard deviation of returns would be high, dragging down the Sharpe ratio. But since the large moves are to the upside, the downside deviation would be much lower, resulting in a more favorable Sortino ratio. The Sortino ratio better reflects this strategy's actual risk profile.
Interpreting the Sortino ratio
Like the Sharpe ratio, higher values are better. However, because downside deviation is typically smaller than total standard deviation, Sortino ratios tend to be numerically higher than Sharpe ratios for the same strategy. A Sortino ratio of 2 or above is generally considered good, while values above 3 are excellent. Direct comparison should only be made between Sortino ratios calculated using the same MAR and time period.
Practical example
Assume a strategy returns 12% annually with a risk-free rate of 4%. If the strategy has a total standard deviation of 10% and a downside deviation of 7%, the Sharpe ratio would be (12 - 4) / 10 = 0.8, while the Sortino ratio would be (12 - 4) / 7 = 1.14. The Sortino ratio gives the strategy more credit because much of its volatility comes from positive returns. This difference becomes even more pronounced for strategies with positively skewed return distributions, such as long volatility or trend-following approaches.
Relationship to other metrics
The Sortino ratio complements other risk metrics rather than replacing them. While it provides a better view of downside risk than the Sharpe ratio, it does not capture tail risk or maximum drawdown. A comprehensive evaluation should include the Sortino ratio alongside maximum drawdown (for worst-case loss), the Calmar ratio (return per unit of drawdown), and visual inspection of the equity curve.
How Tektii helps
Tektii calculates the Sortino ratio alongside the Sharpe ratio and other risk-adjusted metrics for every backtest. The platform lets traders set custom minimum acceptable return thresholds and compare strategies using the metric that best matches their risk preferences. By presenting multiple risk perspectives simultaneously, Tektii helps traders avoid over-reliance on any single metric when evaluating strategy performance.