Sortino Ratio vs Sharpe Ratio: Which Should You Use?

The Sortino ratio and Sharpe ratio both measure how much return you're generating per unit of risk. The difference is in how they define risk: the Sharpe ratio penalizes all volatility, while the Sortino ratio penalizes only downside volatility.

For most active traders, the Sortino ratio is the more useful metric.

The Core Difference

Sharpe ratio uses the total standard deviation of your returns — both good months and bad months drag down the score equally.

Sortino ratio uses only the standard deviation of negative returns. Good months don't count against you.

Sharpe  = (Return − Risk-Free Rate) / Total Standard Deviation

Sortino = (Return − Risk-Free Rate) / Downside Standard Deviation

A portfolio that has a few monster up months alongside steady returns will score better on Sortino than Sharpe, because those big gains are no longer penalized.

When This Distinction Matters

Imagine two portfolios over 12 months:

Portfolio A — Steady grinder: Monthly returns: +2%, +1.5%, +1.8%, +2.1%, +1.9%, +1.6%, +2.0%, +1.7%, +1.8%, +2.0%, +1.5%, +1.9%

Portfolio B — Momentum with occasional blowouts: Monthly returns: +8%, -2%, +6%, -1%, +9%, -3%, +7%, -1%, +8%, -2%, +7%, -1%

Portfolio B has higher volatility — its standard deviation is much larger. But the volatility is mostly upside volatility. Its Sharpe ratio will be penalized for those +8% and +9% months the same way a portfolio with big losing months would be penalized.

The Sortino ratio only penalizes the -1%, -2%, and -3% months. Portfolio B's Sortino will reflect that its downside is actually quite contained.

A Worked Comparison

Let's use simplified numbers. Assume annual return = 20%, risk-free rate = 4%, and:

• Total annualized standard deviation = 18%
• Downside annualized standard deviation = 8% (only the losing months)

Sharpe  = (20% − 4%) / 18% = 0.89
Sortino = (20% − 4%) / 8%  = 2.00

Same portfolio, same returns — but the Sortino ratio is more than twice the Sharpe. Neither is "wrong." They're measuring different things.

Summary Comparison

Which Should You Use?

Use the Sharpe ratio when:

• Comparing your portfolio against benchmarks or other managers (it's the industry standard)
• You care about total volatility — for example, if you're investing on margin and oscillations have cash flow implications
• You want a metric that others will recognize and trust

Use the Sortino ratio when:

• Your strategy is designed to generate asymmetric returns (more upside than downside)
• You're evaluating a momentum or trend-following approach where large up months are expected
• You want a metric that better reflects the experienced quality of the ride

The honest answer: use both. A strategy that looks good on Sharpe but mediocre on Sortino suggests that its "good" volatility isn't as clean as you think. A strategy that looks great on Sortino but poor on Sharpe is delivering return unevenly — lots of upside spikes, meaning the gains are lumpy and unpredictable.

The Misconception to Avoid

A Sortino ratio is almost always higher than the Sharpe ratio for the same portfolio, because it uses a smaller denominator. This does not mean Sortino is more forgiving or that you should use it to make your strategy look better. Both numbers have context that requires the other.

If someone quotes only a Sortino ratio, ask what the Sharpe is. If they quote only a Sharpe, ask what the Sortino is. A full picture requires both.

How AlphaLens Calculates Both

AlphaLens displays both Sharpe and Sortino in the metrics panel, computed from your actual daily return history. The downside deviation uses a 0% minimum acceptable return threshold — only return periods below zero contribute to the denominator — which is the most conservative and most common convention.

Connect your Alpaca or IBKR account to see both metrics for your portfolio.