Every quant eventually stumbles across the Sortino ratio and thinks they've found something cleaner than Sharpe. No penalty for upside volatility — brilliant. But here's the part most tutorials skip entirely: the number you get depends enormously on a threshold you probably set without thinking twice. That threshold is called the Minimum Acceptable Return, or MAR, and it quietly controls everything.

The direct answer is this — the Sortino ratio is not a fixed, objective number. It is a function of whatever MAR you choose. Set it to zero, and you penalise only negative returns. Set it to the risk-free rate, and you're measuring something different. Set it to your fund's hurdle rate, and you get a third ranking entirely. The same strategy can look excellent or mediocre depending purely on that one input.

CONCEPTThe MAR threshold in Sortino calculations defines what counts as "bad" volatility — and that definition reshapes every strategy comparison you make.
WARNINGComparing Sortino ratios across research papers or platforms is meaningless unless both use an identical MAR — most don't disclose it clearly.
KEY IDEADownside deviation only captures semi-variance below your chosen threshold — shift that threshold and the entire denominator of the ratio changes.

Think of it like judging a runner's performance. If your benchmark is "finishing under four hours," a three-hour-fifty runner looks great. Change the benchmark to three-and-a-half hours, and suddenly they're underperforming. The runner hasn't changed. Your measurement frame has. That's exactly what happens when two analysts compare Sortino ratios using different MARs — they're measuring different things while believing they're comparing the same thing.

Sortino Ratio by MAR Threshold Sortino Ratio 3.0 2.0 1.0 0.0 MAR = 0% MAR = RF Rate MAR = Hurdle Strategy A Strategy B

Frank Sortino's original work specified using the investor's target return as the MAR — not zero, not the risk-free rate. That distinction matters because it anchors the measure to actual investor goals rather than an arbitrary number. When the MAR shifts from zero to a 6% annual hurdle, strategies with modest but consistent returns get penalised more heavily, while high-momentum strategies with occasional sharp drawdowns can leapfrog them in the rankings. The entire leaderboard reshuffles.

Practitioners who use this metric seriously always run their calculations across multiple MAR assumptions and look for strategies that rank well under all of them. That robustness test reveals far more than any single Sortino number ever could. For the deeper mechanics, Investopedia's Sortino ratio breakdown covers the formula clearly, while Wikipedia's Sortino ratio entry traces the academic origins. The broader context of downside risk measurement explains why semi-variance was developed in the first place and what it was trying to fix.

Before quoting or comparing any Sortino ratio, ask one question first: what MAR was used? If nobody can answer that, the number is noise dressed up as signal.

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