Definition
The Sortino ratio is a measure of *risk-adjusted return* that counts only the bad kind of volatility. It is a direct refinement of the Sharpe ratio, and the two formulas look almost identical:
Sortino Ratio = (Portfolio Return − Minimum Acceptable Return) / Downside Deviation
There are three pieces:
- Portfolio return — the total return of the fund or portfolio over a period,
including price change and reinvested distributions.
- Minimum acceptable return (MAR) — the threshold below which you consider a
return a "bad" outcome. Often this is the risk-free rate, sometimes zero, and sometimes a target like your required income yield.
- Downside deviation — how much returns bounced around, but measured using
*only the periods that fell below the MAR*. Returns above the threshold are treated as zero risk.
The one crucial difference from the Sharpe ratio is the denominator. The Sharpe ratio divides by standard deviation, which measures *all* volatility — a big gain counts against a fund just as much as a big loss. The Sortino ratio divides by downside deviation, which ignores upside swings entirely and penalizes a fund only when it drops below your minimum acceptable return. A higher Sortino ratio means more reward for each unit of *harmful* volatility.
Why It Matters
Most investors do not lie awake worrying that their fund went *up* too much. Yet standard deviation — and therefore the Sharpe ratio — treats a surprise 8% monthly gain as exactly as "risky" as a surprise 8% monthly loss. That is mathematically tidy but emotionally and practically backwards. The Sortino ratio fixes this by separating the volatility you fear from the volatility you welcome.
For income and ETF investors this distinction is especially valuable. Many high-yield and dividend-growth strategies are asymmetric: they grind out steady distributions and occasionally jump on a strong month. Under the Sharpe ratio those upside jumps inflate the standard deviation and *lower* the score, making a perfectly pleasant fund look riskier than it feels to own. The Sortino ratio only reacts to the drawdowns that actually threaten your principal and your income stream, which is what a retiree drawing a paycheck from the portfolio genuinely cares about.
It also complements the other risk numbers rather than replacing them. The Sharpe ratio tells you about efficiency against *total* variability; beta tells you how sensitive a fund is to the broad market; and the distribution rate tells you the headline income. The Sortino ratio adds the missing piece: reward per unit of *downside* risk. Reading them together gives a far fuller picture than any single figure.
Example
Consider two funds income investors frequently weigh against each other: SCHD, a low-cost dividend-growth ETF, and JEPI, an equity premium income (covered-call) fund. Covered-call funds like JEPI and its Nasdaq sibling JEPQ sell call options, which *caps* their upside — they hand away the biggest up-months in exchange for option premium. That capped upside is exactly where Sharpe and Sortino diverge.
Suppose over a given year the return and volatility figures work out like this, with a minimum acceptable return of 4%:
- SCHD returns 10%, with total standard deviation of 14% but downside deviation
of only 8% — its volatility is lopsided toward good months.
- JEPI returns 9%, with total standard deviation of 9% and downside deviation of
8% — its swings are small but fairly symmetric, because the covered-call cap trims the upside that would otherwise pull the two deviations apart.
Run the Sharpe ratios first:
- SCHD: (10% − 4%) / 14% = 0.43
- JEPI: (9% − 4%) / 9% = 0.56
By Sharpe, JEPI wins — its low total volatility flatters it. Now run Sortino:
- SCHD: (10% − 4%) / 8% = 0.75
- JEPI: (9% − 4%) / 8% = 0.63
The verdict flips. Once you stop punishing SCHD for its cheerful up-months and measure only the downside, SCHD delivered more return per unit of *harmful* risk. JEPI's advantage under Sharpe was partly an artifact of a covered-call strategy that never surprises you to the upside — so it has little "good volatility" for the Sharpe ratio to penalize in the first place. This is the classic pattern: capped-upside income funds tend to score relatively better on Sharpe than on Sortino, while funds with asymmetric, upside-skewed returns look better on Sortino than on Sharpe.
Common Mistakes
- Comparing Sortino ratios computed with different MARs. The minimum acceptable
return is a free parameter. One fact sheet may use zero, another the T-bill rate, another a 6% income target. Change the MAR and the ratio changes — so two Sortino numbers are only comparable if they share the same threshold.
- Comparing across different time periods. Like every risk-adjusted metric, a
Sortino ratio measured in a calm year looks far better than one measured through a drawdown. Only compare funds over the *same* window.
- Treating it as a standalone verdict. A high Sortino ratio does not tell you a
fund's expense ratio, its tax treatment, how much of the distribution is return of capital, or whether it fits your goals. It is one input, not a buy signal.
- Assuming Sortino always beats Sharpe. It is not "the better ratio," just a
different lens. For a symmetric, broadly diversified fund the two often tell nearly the same story; the gap only widens when returns are skewed.
- Chasing tiny differences. A Sortino ratio of 0.75 versus 0.72 is noise. Use it
to separate clearly efficient funds from clearly inefficient ones, not to split hairs.
FAQ
What is a good Sortino ratio?
As a rough guide, a Sortino ratio below 1.0 is considered sub-par, 1.0 to 2.0 is good, 2.0 to 3.0 is very good, and above 3.0 is excellent. Because it ignores upside volatility, a fund's Sortino ratio is usually *higher* than its Sharpe ratio, so do not compare the two numbers head-to-head against the same threshold. As always, compare a fund against its peers over the same time frame and using the same minimum acceptable return rather than against a fixed cutoff.
Sortino vs Sharpe — which is better?
Neither is universally better; they answer different questions. The Sharpe ratio rewards funds for low *total* volatility, which suits investors who dislike surprises in either direction. The Sortino ratio rewards funds for low *downside* volatility only, which suits income investors who are happy to keep upside surprises. For funds with lopsided, upside-skewed returns the Sortino ratio is often the fairer measure; for symmetric funds the two usually agree.
Can the Sortino ratio be negative?
Yes. A negative Sortino ratio means the fund's return fell *below* your minimum acceptable return over the period — the numerator is negative. It does not necessarily mean the fund lost money in absolute terms; it can simply mean the return failed to clear the threshold you set, whether that threshold is zero, the risk-free rate, or an income target.
Why is downside deviation different from standard deviation?
Standard deviation measures how far *all* returns spread around their average, so a big gain and a big loss both increase it. Downside deviation only measures the spread of returns that fall *below* the minimum acceptable return, treating every above-threshold period as zero risk. That is why two funds can share the same standard deviation but have very different downside deviations if one's volatility is concentrated in good months rather than bad ones.