Think of it like judging a road trip by counting potholes instead of every bump in the road. A car that jolts you upward over a speed bump isn't the problem. The pothole that jars your coffee out of the cup is. The Sharpe ratio counts both. The Sortino ratio counts only the pothole.
In this guide, you'll learn what the Sortino ratio measures, why it matters for anyone comparing funds or strategies, how to calculate it step by step, and how to read it using real fund and index data. You'll also see the most common mistakes investors make when applying it, plus answers to the questions people ask most.
VOO's one-year Sortino ratio of 2.05, screenshotted from PortfoliosLab on September 27, 2026.
What Is the Sortino Ratio?
The Sortino ratio is a risk-adjusted performance metric that measures how much return an investment generates for each unit of downside risk it takes on. It was developed by Frank Sortino and introduced in a 1994 paper in the Journal of Investing as an alternative to the older Sharpe ratio.
The formula is straightforward: Sortino Ratio = (Portfolio Return - Minimum Acceptable Return) / Downside Deviation.
The minimum acceptable return (MAR) is a threshold you choose, often the risk-free rate, zero, or a target return like 5% a year. Any return below that threshold counts as bad. Anything above it doesn't count against the investment at all.
Downside deviation is the key difference from the Sharpe ratio. Instead of measuring how much all returns bounce around their average, which is what standard deviation does, downside deviation only measures the spread of returns that fall below the MAR. A month where a fund gains 8% doesn't get punished, even though that is technically volatility. A month where it loses 8% does.
This distinction matters because most investors don't actually mind upside surprises. You are not worried about a holding that gains more than expected. You are worried about the one that loses more than expected. The Sortino ratio was built to match that intuition, scoring an investment on the volatility that actually threatens your goals rather than volatility in general. For more background on how the ratio was derived and how it is applied across the industry, see Wikipedia's overview of the Sortino ratio.
Why the Sortino Ratio Matters
The Sharpe ratio has been the industry default since the 1960s, and it's still useful. But it has a well-documented blind spot: it treats an unexpected 10% monthly gain exactly the same as an unexpected 10% monthly loss. Both increase the standard deviation in the denominator and drag the ratio down.
That blind spot becomes a real problem for strategies with asymmetric return patterns. A covered call fund that regularly clips a portion of its upside will look artificially smooth to the Sharpe ratio. Buffer ETFs, which cap gains in exchange for downside protection, are a clear example. Several of them post Sortino ratios above 7, far higher than a plain S&P 500 index fund, largely because almost none of their remaining return variation sits on the downside.
2.05 vs 1.90 is the current one-year Sortino ratio gap between VOO and the raw S&P 500 index, a reminder that even a simple index fund can look meaningfully better or worse depending on which ratio you check.
For anyone comparing actively managed funds or option-based ETFs, relying on the Sharpe ratio alone can rank a genuinely steadier fund below a choppier one just because the steadier fund also had strong up months. The Sortino ratio corrects for that. If you're still working out how much of this volatility you can personally stomach, MoneyFlock's guide to finding your risk tolerance is a useful starting point before you lean too hard on either ratio.
How to Calculate the Sortino Ratio
Calculating the Sortino ratio by hand takes five steps. Most brokerage platforms and portfolio trackers calculate it automatically, but understanding the mechanics helps you sanity check the number and know when it's being skewed by a short data window.
Step 1: Gather Your Return Data
Collect a series of periodic returns, monthly is standard, for at least three years. Institutional training providers like Wall Street Prep recommend a minimum of 24 to 36 monthly data points so a couple of unusually good or bad months don't dominate the result. Using only the trailing 12 months, the way many free stock screeners default to, can make a ratio swing wildly from quarter to quarter.
Step 2: Choose Your Minimum Acceptable Return
Pick a MAR that matches your goal. Common choices are 0% (any loss counts as downside), the risk-free rate, or a personal target return like 6% a year. The MAR is subjective, so always check what MAR a published Sortino ratio is using before comparing it to another one calculated differently.
Step 3: Isolate the Downside Returns
Go through each period's return and keep only the ones that fall below your MAR. If your MAR is 0% and a fund returns -2%, -1%, 3%, -4%, and 5% across five months, only -2%, -1%, and -4% count as downside periods. The two positive months are dropped entirely from the risk calculation, which is the core mechanical difference from the Sharpe ratio.
Step 4: Calculate Downside Deviation
Square each downside shortfall, average the squared values across all periods, including the ones that were zero because they landed above the MAR, then take the square root. This is the downside deviation, and it is typically annualized by multiplying by the square root of 12 for monthly data.
Step 5: Apply the Formula and Annualize
Subtract the MAR from your average annualized return, then divide by the annualized downside deviation: Sortino Ratio = (Annualized Return - MAR) / Annualized Downside Deviation.
A result above 1.0 is generally considered acceptable, above 2.0 is good, and above 3.0 is excellent, similar to how Sharpe ratio bands are read. The two numbers are not directly comparable to each other, though, because they use different denominators.
The three inputs behind the Sortino ratio formula, screenshotted from Wall Street Prep's investment analysis guide.
Real Examples
Real fund data shows how differently the Sortino ratio can rank investments compared to a gut-feel read of volatility. As of September 27, 2026, according to PortfoliosLab:
Table: One-Year Sortino Ratio, Selected Funds and Benchmarks
Table: When the Sortino Ratio Can Mislead You
The buffer ETFs in the first table post Sortino ratios roughly four times higher than a plain index fund. That doesn't mean they are four times better investments. It means their structure, capping gains in exchange for a downside floor, removes most of the return variation the Sortino ratio is designed to penalize. A Sharpe ratio comparison would flatten this gap somewhat, since it also counts the capped upside as a cost.
8.70 is CPSP's one-year Sortino ratio, roughly four times a plain index fund's, largely because its capped-gain structure removes most upside volatility from the calculation entirely.
Always confirm the MAR and lookback window before comparing two Sortino ratios pulled from different sources, since neither is standardized across the industry.
Common Mistakes
Mistake 1: Comparing Ratios With Different MARs
Two screeners can list wildly different Sortino ratios for the same fund simply because one uses a 0% MAR and the other uses a risk-free-rate MAR. Before comparing funds across two different websites or reports, confirm which minimum acceptable return each one used. If you can't find it, treat the numbers as directionally useful rather than precisely comparable.
Mistake 2: Using Too Short a Time Window
1994 is the year Frank Sortino first published the ratio in the Journal of Investing, decades before it became a default filter on brokerage screeners. Despite that long history, many free tools still calculate it over just the trailing 12 months. A single unusually calm or volatile year can swing the ratio significantly. Where possible, check the 3-year or 5-year Sortino ratio alongside the 1-year figure, the way PortfoliosLab lists all three side by side.
PortfoliosLab's 1Y, 5Y, and 10Y Sortino ratio comparison table for VOO and buffer ETF peers, captured September 27, 2026.
Mistake 3: Treating a High Sortino Ratio as Risk-Free
A Sortino ratio above 5 or 8, like the buffer ETFs shown earlier, does not mean an investment is free of risk. It usually means the return profile is structurally shaped, through options overlays or return caps, in a way that removes most of the variance the formula measures. Read the fund's actual strategy and expense ratio before assuming a high ratio equals a safe holding.
Mistake 4: Ignoring the Sharpe Ratio Entirely
The Sortino ratio does not replace the Sharpe ratio, it complements it. If you're deciding between two funds, look at both. A fund with a strong Sortino ratio but a mediocre Sharpe ratio may have a return pattern that is choppier on the upside than you'd expect, which matters if you plan to withdraw from the account regularly. For a deeper walkthrough of that companion metric, see MoneyFlock's guide to the Sharpe ratio.
Frequently Asked Questions
What Is a Good Sortino Ratio?
Most practitioners treat a Sortino ratio above 1.0 as acceptable, above 2.0 as good, and above 3.0 as excellent, mirroring the bands used for the Sharpe ratio. Context still matters. A conservative bond fund and an aggressive growth fund shouldn't be judged on the same scale, since their downside deviation naturally differs.
How Do You Calculate the Sortino Ratio Step by Step?
Subtract your minimum acceptable return from the investment's average annualized return, then divide the result by the annualized downside deviation, which only reflects returns that fell below that same MAR. See the step-by-step walkthrough earlier in this guide for the full five-step process.
Is the Sortino Ratio Better Than the Sharpe Ratio?
Neither is strictly better. The Sortino ratio is more useful when a strategy has an asymmetric return pattern, like options-based or buffer ETFs. The Sharpe ratio remains the more widely reported, standardized figure, which makes it easier to find and compare across a broad list of funds.
Can the Sortino Ratio Be Negative?
Yes. If an investment's return falls below its minimum acceptable return, the numerator becomes negative, and the resulting Sortino ratio will also be negative, regardless of how small the downside deviation is. A negative Sortino ratio signals the investment failed to clear its own minimum bar over the measured period. For a plain-language walkthrough of downside risk with a worked example, Schwab's guide to the Sortino ratio is a solid companion read.
Key Takeaways
Circling back to the road trip: the Sharpe ratio counts every bump, up and down. The Sortino ratio only counts the potholes. Neither view is wrong, they just answer different questions, and reading both gives you the fullest picture of what an investment's return pattern actually feels like to hold.
- The Sortino ratio only penalizes downside deviation, returns below your chosen minimum acceptable return (MAR), unlike the Sharpe ratio, which penalizes all volatility equally.
- A ratio above 1.0 is acceptable, above 2.0 is good, and above 3.0 is excellent, though bands should be read alongside a similar MAR and lookback window.
- As of September 2026, VOO's one-year Sortino ratio (2.05) sits above the S&P 500 index itself (1.90), and above the 1.47 median across all funds PortfoliosLab tracks.
- Capped-upside products like buffer ETFs can post Sortino ratios above 7 or 8, which reflects their structure more than genuine safety.
- Always confirm the MAR and time window before comparing Sortino ratios pulled from two different sources.
- Use the Sortino ratio alongside the Sharpe ratio and maximum drawdown rather than in isolation, for a fuller picture of an investment's risk.
- When the Sortino and Sharpe ratios disagree on a fund, that disagreement itself is useful information about the shape of its returns.