Contents
Sortino Ratio is a risk-adjusted return metric that improves on the Sharpe Ratio by penalising only downside volatility — the volatility that investors actually dislike — rather than total standard deviation (which treats upside and downside equally).
Formula
Sortino = (Rp − Rf) / σd
Where: Rp = annualised portfolio return, Rf = risk-free rate (the conventional name for the short-term sovereign yield used as a benchmark; same period-average T-bill rate as used in Sharpe), σd = downside deviation — the standard deviation computed using only returns below a target threshold T (typically T = Rf or T = 0).
σd = √[ (1/N) × Σ min(Ri − T, 0)² ]
Only periods where the return falls below the threshold contribute to σd. Periods with returns above T contribute zero to the denominator.
Why Sortino Outperforms Sharpe for Non-Normal Returns
Indian equity mutual funds exhibit negative skew: markets fall faster than they rise (2008, 2020, 2022 corrections all show larger daily drawdowns than the equivalent upsides). Sharpe penalises a fund that has high positive-return months equally with one that has high negative-return months, even though the positive volatility is welcome. Sortino separates these: a fund can have high upside volatility and a high Sortino ratio simultaneously. SEBI Circular 2021/647 requires disclosure of standard deviation and Sharpe; Sortino is typically computed by analytics providers (Value Research, AdvisorKhoj, Morningstar India).
Worked Example (Indian Context)
Mirae Asset Large Cap Fund – Direct Plan, 3-year monthly return data: annualised return 17.2%, annualised downside deviation (T = 0%) = 9.8%, period-average T-bill Rf = 4.4%.
Sortino = (17.2 − 4.4) / 9.8 = 12.8 / 9.8 = 1.31
Compare Sharpe (same fund, σtotal = 15.1%): (17.2 − 4.4) / 15.1 = 0.85
The Sortino of 1.31 vs Sharpe of 0.85 signals that the fund's total volatility is dominated by upside months — the downside risk is proportionally lower, a desirable characteristic. A fund showing Sortino < Sharpe would indicate its volatility is concentrated in losses.
Interpretation
| Sortino Range | Signal |
|---|---|
| < 0.5 | High downside risk relative to excess return |
| 0.5 – 1.0 | Moderate; acceptable for equity category |
| 1.0 – 2.0 | Strong downside control; consistent positive skew |
| > 2.0 | Exceptional; verify NAV data for smoothing artifacts |
Caveats
Sortino is sensitive to the threshold T chosen. Setting T = 0 vs T = Rf changes σd and therefore the ratio. Industry convention is T = 0 (zero-return threshold) for most Indian screener platforms, but AdvisorKhoj uses T = Rf. Always confirm which threshold is used before comparing Sortino across platforms.
Related terms: Sharpe Ratio, Standard Deviation, Alpha, Volatility, Rolling Returns.
Primary source: Sortino & van der Meer (1991), "The Downside Risk", Journal of Portfolio Management. SEBI Circular SEBI/HO/IMD/DF2/CIR/P/2021/647 (risk ratio disclosure framework).
Past performance is not indicative of future returns. Mutual fund investments are subject to market risks. Read all scheme-related documents carefully. ARN-314872. APMI APRN-01658. Content is informational and not investment advice.