Sharpe Ratio
Definition
The Sharpe Ratio measures risk-adjusted return. It divides the excess return earned above the risk-free rate by the standard deviation of those returns.
Sharpe Ratio = (Portfolio Return - Risk-Free Rate) / Standard Deviation of Returns
A higher Sharpe Ratio indicates better risk-adjusted performance: more return per unit of risk taken. A ratio above 1.0 is generally considered acceptable; above 2.0 is strong. These benchmarks are context-dependent and should not be applied mechanically.
Note: The risk-free rate used varies by currency and time period (commonly a short-dated government bill yield). Comparisons across periods or currencies require a consistent risk-free rate assumption.
Why It Matters
Raw return figures can be misleading if they are achieved by taking excessive risk. A fund returning 20% per year through highly leveraged concentrated positions is not comparable to one returning 12% through a diversified, lower-risk strategy.
The Sharpe Ratio normalises returns by the volatility of achieving them, enabling fairer comparison across strategies with different risk profiles. It is the most widely reported risk-adjusted metric for liquid alternative strategies, particularly hedge funds.
Illustrative example:
Hedge Fund A: Returns 10% per year, standard deviation of 8%, risk-free rate 4%. Sharpe = (10% - 4%) / 8% = 0.75
Hedge Fund B: Returns 7% per year, standard deviation of 2%, risk-free rate 4%. Sharpe = (7% - 4%) / 2% = 1.50
Fund B has a higher Sharpe Ratio despite lower absolute return. Depending on an investor’s risk mandate, Fund B may be preferable.
Limitations in Alternatives
The Sharpe Ratio has four significant limitations when applied to alternative investments.
1. Smoothed Returns and Stale Pricing
Private market assets are valued infrequently — typically quarterly, or even annually for real estate. Because valuations do not move daily, the standard deviation of reported returns is artificially low. A private equity fund might report quarter-on-quarter NAV changes of +2%, +3%, -1%, +4%, producing a very low standard deviation — even though the underlying companies would show much higher volatility if listed.
This mechanically inflates the Sharpe Ratio for any fund with infrequent valuations. A Sharpe of 2.0+ for a private credit fund may say more about the smoothness of mark-to-model valuations than about the true risk-adjusted quality of returns. See Valuation Risk and NAV.
2. Non-Normal Return Distributions
The Sharpe Ratio assumes returns are normally distributed around their mean. Many alternative strategies have “fat tails” — rare but extreme losses that standard deviation does not capture.
A strategy that earns steady small gains by selling insurance-like protection (e.g., certain options strategies, some hedge fund strategies) may show an excellent Sharpe Ratio until a stress event produces a catastrophic loss. The Sharpe Ratio would not have warned of this risk, because tail events are outside the range that standard deviation measures well.
For strategies with known tail risk, the Sortino Ratio (which only penalises downside volatility) or maximum drawdown analysis are more informative complements.
3. Short Track Records
Calculating a statistically reliable Sharpe Ratio requires enough return observations to estimate a stable mean and standard deviation. Most private funds have quarterly NAV data over 7—12 years — producing at most 28—48 data points. This is insufficient for statistical confidence. Sharpe Ratios calculated on short return series can vary substantially depending on which period is chosen.
4. Illiquidity and Actionability
The Sharpe Ratio assumes that investors can respond to changes in the risk profile of their investment — reducing or exiting positions when risk rises. In locked-up funds with 7—12 year terms and no secondary market access, this assumption is false. A high Sharpe Ratio is less meaningful if the investor cannot exit when conditions deteriorate.
When the Sharpe Ratio Is Useful
The Sharpe Ratio is most appropriate for:
- Liquid alternative strategies — hedge funds, commodity trading advisors (CTAs), liquid multi-asset strategies, where returns are calculated from daily or weekly marks and trade execution is possible
- Comparing similar strategies — comparing two long/short equity hedge funds using the same return frequency and risk-free rate
- Quick screening — as a first-pass filter when comparing strategies of similar type
It is least appropriate for illiquid private markets (private equity, infrastructure, private credit, real estate) where reported volatility is structurally understated by valuation smoothing.
Related Files
Manual Review Notes
- The “above 2.0 is excellent” benchmark is informal and context-dependent. In low-rate environments, even a Sharpe of 0.5 may be acceptable. Avoid presenting this as a universal standard.
- Variants of the Sharpe Ratio (Sortino, Calmar, Omega) address specific limitations. These are not covered here but may warrant a brief note in a future expansion.
- The Sharpe Ratio uses standard deviation as the risk measure. This is appropriate for symmetric, roughly normal distributions; less so for skewed or fat-tailed distributions typical of some hedge fund strategies.