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Start Learning → Browse All Articles →Most traders don't actually mind upside volatility — the Sortino ratio is built around that simple, intuitive observation.
The Sharpe ratio treats every deviation from the average return — whether a sharp gain or a sharp loss — as equally undesirable “risk.” Most traders and investors don’t actually feel this way in practice: a strategy that occasionally posts unusually large gains isn’t something anyone complains about, even though it inflates the strategy’s measured volatility just as much as an equally large loss would. The Sortino ratio, named after economist Frank Sortino, was built specifically to address this mismatch.
Like the Sharpe ratio, the Sortino ratio starts with excess return over a risk-free rate, but instead of dividing by total standard deviation, it divides by downside deviation — a measure that only counts the variability of returns that fall below a chosen target or minimum acceptable return, typically zero or the risk-free rate. Upside swings above that target are simply excluded from the risk calculation entirely.
Strategies with asymmetric payoff profiles, such as option-selling strategies that collect small premiums regularly with occasional larger losses, or strategies that occasionally capture large directional moves, are exactly the kind of case where Sharpe and Sortino ratios can tell noticeably different stories. A strategy could show a mediocre Sharpe ratio due to occasional large gains inflating its volatility measure, while showing a much stronger Sortino ratio once only the downside variability is counted.
One practical decision when calculating a Sortino ratio is choosing the threshold below which a return counts as “downside” — some use zero, others use the risk-free rate, and some use a specific target return relevant to their goals. This choice affects the resulting number, so it’s worth being explicit about which threshold you’re using when comparing Sortino ratios across strategies or time periods.
The Sortino ratio doesn’t replace the Sharpe ratio so much as add a second lens; a trader who wants a fuller risk picture often benefits from looking at both, particularly for strategies with known asymmetric or skewed return distributions rather than roughly symmetric ones.