How the Sortino Ratio Is Calculated
The Sortino ratio shares a similar structure to the Sharpe ratio but replaces the denominator, total standard deviation, with downside deviation, the volatility measured only from returns that fall below a target (often zero). Large upside moves are not counted as risk at all.
What the Sharpe Ratio Misses: Penalizing Upside
Because the Sharpe ratio treats all volatility, up or down, as equally risky, a strategy prone to occasional sharp rallies can see its standard deviation, and therefore its Sharpe ratio, unfairly penalized. Critics have long argued that punishing upside surprises as ‘risk’ runs counter to investor intuition, which is exactly what the Sortino ratio was designed to address.
When the Two Metrics Diverge Sharply
Strategies that let winners run while cutting losses short, such as trend-following approaches, tend to show a much higher Sortino ratio than Sharpe ratio. Strategies with roughly symmetric up and down swings show far less divergence between the two.
Which Metric Should You Prioritize
For investors who prioritize avoiding losses, the Sortino ratio may better reflect the risk they actually feel. Comparing both together, and noting how far apart they are, can reveal whether a strategy has an asymmetric return profile worth understanding before committing capital.
| Metric | Sharpe Ratio | Sortino Ratio |
|---|---|---|
| Denominator | Total volatility (std dev) | Downside deviation only |
| Treats upside swings as | Risk (penalized) | Not risk |
| Best fit | Symmetric return strategies | Asymmetric (skewed-upside) strategies |
Frequently Asked Questions
Is the Sortino ratio always higher than the Sharpe ratio?
Generally yes, since it only counts downside volatility, but it’s not guaranteed in every case, the outcome depends on the actual shape of the return distribution.
How is the target return (MAR) set?
Some analysts use 0% as the threshold for any loss, others use the risk-free rate or a custom minimum acceptable return, and the choice of threshold changes the resulting ratio.
Why look at both metrics together?
The Sharpe ratio gives a picture of overall stability, while the Sortino ratio focuses specifically on downside risk, so viewing both together reveals whether a strategy’s return profile is asymmetric.
Can individual investors calculate this themselves?
Yes, with monthly return data in a spreadsheet, downside deviation can be calculated by isolating only the negative-return months and computing their standard deviation.
Key Takeaways
The Sortino ratio refines the Sharpe ratio by only penalizing downside volatility, leaving upside swings untouched, which makes it a useful complement for evaluating strategies with asymmetric return profiles. Comparing the two together reveals more about a strategy’s true risk character than either alone. This article is for informational purposes only and does not constitute investment advice.
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