Risk & volatility

Sortino ratio

Sortino ratio is a measure of return above a chosen target per unit of downside deviation, counting returns below the target rather than all fluctuations as risk.

What it means

The Sortino ratio compares a portfolio’s average return with a chosen target while focusing on returns that fall short of that target. It is usually calculated from a history of periodic returns, such as monthly returns. A higher ratio means more return above the target relative to the downside deviation measured over that history; it does not establish what will happen next.

Unlike the Sharpe ratio, which uses the standard deviation of all returns, the Sortino ratio does not treat above-target returns as downside risk. That distinction can be useful when an investor cares more about falling short of a goal than about returns varying in either direction.

How it is calculated

For equally spaced returns, one common version is:

Sortino ratio = (mean(R) − T) / sqrt[sum(min(0, R_i − T)^2) / N]

  • R_i is the return in period i, expressed as a decimal; 2% is 0.02.
  • mean(R) is the arithmetic average of all the periodic returns, not just the below-target ones.
  • T is the target return per period, in the same units as R_i. It might be zero or a periodic minimum acceptable return.
  • N is the number of periods. The square-root expression is downside deviation: only shortfalls contribute to the squared sum, but the sum is divided by all N periods.

The numerator and denominator are both returns per period, so the ratio has no units. Other published conventions exist, including different denominators for downside deviation; ratios calculated under different conventions should not be compared without adjustment. If downside deviation is zero, the ratio is undefined, not a finite score.

Worked example

Suppose a hypothetical portfolio has four monthly returns: +4%, +2%, −2% and 0%. Set the monthly target at 0%.

  1. Average monthly return: (4% + 2% − 2% + 0%) / 4 = 1%.
  2. Shortfalls below the target: only −2% contributes. The other three periods contribute zero.
  3. Downside deviation: sqrt[(0² + 0² + (−2%)² + 0²) / 4] = 1% per month.
  4. Sortino ratio: (1% − 0%) / 1% = 1.

This is a monthly ratio calculated from only four observations, not an annual ratio or a reliable estimate of future results. Using a different target would change both the numerator and the downside deviation.

Why it matters before you trade

A historical Sortino ratio can help frame whether a portfolio’s recorded returns have compensated for falling below a specified target. Before comparing portfolios, check that they use the same return frequency, time span, target and calculation convention. Short histories can make the figure particularly sensitive to a single loss.

The ratio also leaves important questions unanswered: it does not show the size of a prospective order, whether the stock can be traded efficiently, or how a new position changes portfolio concentration. Trading costs can reduce realized returns, so a return series that omits them may overstate the return available after execution.

How PreTrAIde uses it

The product facts do not say that PreTrAIde calculates or uses the Sortino ratio. Its pre-trade analysis instead evaluates a proposed stock basket before an order is placed, including estimated spread, market impact, daily volatility, 1-day 95% value at risk and portfolio breakdowns. It returns a GO, NO-GO or MODIFY verdict with supporting reasoning; those verdicts are decision support, not recommendations. These checks address aspects of a proposed trade that a historical Sortino ratio does not measure.

Common mistakes

  • Counting only losing periods in the denominator: In the formula above, divide the squared shortfalls by all periods, including periods at or above the target.
  • Mixing time units: A monthly target belongs with monthly returns. Do not label a monthly ratio as annual without a stated conversion method and assumptions.
  • Comparing unlike targets: A zero-target ratio and a ratio using a positive minimum acceptable return answer different questions.
  • Treating it as a complete risk measure: Downside deviation summarizes historical shortfalls; it does not describe every tail event, maximum drawdown or execution cost.

Frequently asked questions

What is the difference between the Sortino ratio and the Sharpe ratio?

Both compare average return with a benchmark or target. The Sortino ratio divides excess return by downside deviation; the Sharpe ratio divides it by the standard deviation of all returns.

What is a good Sortino ratio?

There is no universal cutoff. Interpretation depends on the target, return frequency, sample period and calculation convention, as well as how much data supports the estimate.

Can the Sortino ratio be negative?

Yes. When average return is below the target and downside deviation is greater than zero, the ratio is negative; when downside deviation is zero, the ratio is undefined.

Related terms

Sharpe ratio Sharpe ratio is a measure of historical excess return per unit of return volatility, calculated as average return minus the risk-free rate, divided by the standard deviation of returns. Standard deviation Standard deviation is a measure of how widely observations, such as daily stock returns, vary around their average, expressed in the same units as those observations. Volatility Volatility is a measure of how widely an asset’s returns vary over a specified period, usually expressed as the standard deviation of returns. Expected shortfall (CVaR) Expected shortfall (CVaR) is the average loss in the worst specified fraction of outcomes over a stated time horizon, assuming a defined loss distribution. Drawdown Drawdown is the percentage decline in an investment or portfolio from its previous peak value to a later value before that peak is regained. Pre-trade analysis Pre-trade analysis is the assessment of a proposed stock order or basket before placement, estimating execution costs, liquidity and risk to inform the investor’s decision and execution approach.

Risk & volatility

Historical volatility Implied volatility Annualized volatility Daily volatility Parkinson volatility estimator Yang-Zhang volatility estimator GARCH model Value at risk (VaR) All glossary terms →

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Educational content, not investment advice. PreTrAIde is analysis software, not a broker: it never executes orders, and its verdicts are decision support, not recommendations to buy or sell.