Finance
2 min read

Sharpe Ratio

A measure of risk-adjusted return, calculated as excess return over the risk-free rate divided by standard deviation. Higher is better; the Sharpe ratio lets investors compare strategies on equal footing.

How Sharpe is calculated

Sharpe Ratio = (Portfolio Return − Risk-Free Rate) / Standard Deviation of Returns

A portfolio returning 10% with 15% volatility, against a 4% risk-free rate:

Sharpe = (10 − 4) / 15 = 0.40

Higher is better. The number captures how much excess return is earned per unit of volatility.

What different Sharpe values mean

Approximate ranges:

  • Below 0.5 — weak.
  • 0.5 - 1.0 — okay.
  • 1.0 - 2.0 — good.
  • Above 2.0 — exceptional.
  • Sustained high Sharpe — usually indicates skill or specific strategy advantage.

Long-term US stock market Sharpe is typically around 0.4-0.6.

Why Sharpe matters

The basic insight:

  • Returns alone don't capture risk taken.
  • High returns with high volatility may not be impressive.
  • Same returns with low volatility indicate stronger strategy.
  • Risk-adjusted comparison more meaningful than raw returns.

Combining with absolute returns gives fuller picture.

Sharpe in practice

A few patterns:

  • Most retail Sharpes are mediocre — often below market.
  • Specific strategies (basis trades, market making) can show high Sharpes for limited periods.
  • Sustained high Sharpes are rare and valuable.
  • Sample size matters — Sharpe estimated from short windows is unreliable.

Limitations

Several real concerns:

  • Assumes normal distribution — real returns have fat tails.
  • Treats upside and downside symmetrically — most investors care more about downside.
  • Sortino ratio — variant using only downside volatility.
  • Time period dependence — different windows give different Sharpes.
  • Manipulation — short-vol strategies can produce high Sharpes that mask catastrophic tail risk.

For these reasons, Sharpe is one input among multiple risk-adjusted measures.

What individuals should know

For investors:

  • Don't focus solely on returns — consider volatility.
  • Sharpe is useful for cross-strategy comparison.
  • Watch for tail risk — high Sharpe doesn't always reveal it.
  • Personal portfolio Sharpe is rarely calculated but might be informative.

For most retail using index funds, Sharpe analysis isn't necessary. For evaluating active strategies or comparing alternatives, Sharpe provides useful framework.

The basic principle: more return per unit of risk is better. Sharpe ratio quantifies this in standardized way that allows cross-strategy comparison.