Sharpe Ratio — What is the Sharpe Coefficient?

What is the Sharpe Ratio?

The Sharpe Ratio (Sharpe coefficient) is a measure of risk-adjusted return. It tells you how much additional return you get for each unit of risk you take.

Created by William Sharpe (Nobel Prize winner in Economics) in 1966.

Quick Answer

The Sharpe Ratio is a measure of risk-adjusted return, telling you how much excess return above the risk-free rate you earn per unit of risk. It is calculated as (Rp − Rf) / σp, dividing the portfolio return minus the risk-free rate by the standard deviation of returns. Values below 0.5 are weak, 0.5–1.0 good, 1.0–2.0 very good and above 2.0 excellent (rarely sustained); the S&P 500 sits historically around 0.4–0.6. It assumes normal returns and treats up and down volatility equally. This is educational information, not investment advice.

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Formula

Sharpe Ratio = (Rp - Rf) / σp

Where:

• Rp — average portfolio return
• Rf — risk-free rate (e.g., Polish government bond yields)
• σp — standard deviation of returns (volatility)

Example

Portfolio A: 12% return, 15% volatility, 4% risk-free rate

Sharpe = (12% - 4%) / 15% = 0.53

Portfolio B: 8% return, 5% volatility, 4% risk-free rate

Sharpe = (8% - 4%) / 5% = 0.80

Portfolio B has a better Sharpe Ratio — despite lower return, it gives more per unit of risk.

Value Interpretation

Historically, the S&P 500 has a Sharpe Ratio of around 0.4–0.6 in the long term.

What is it used for?

• Comparing funds/ETFs — which gives better risk-adjusted return?
• Strategy evaluation — does adding a new asset improve portfolio Sharpe?
• Backtesting — key metric when testing historical strategies.

Limitations

1. Assumes normal return distribution — in reality, markets have "fat tails" (black swans).
2. Treats upward and downward volatility equally — large gains "penalize" Sharpe Ratio, though investors enjoy them.
3. Time period dependent — Sharpe Ratio for 1 year vs 10 years can differ drastically.
4. Risk-free rate changes — in zero interest rate era (2020–2021), Sharpe was artificially inflated.

Alternatives

• Sortino Ratio — like Sharpe, but only measures "downside" volatility (downside deviation). Better measure for investors who only care about losses.
• Calmar Ratio — return divided by maximum drawdown.

How can Freenance help?

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Related Articles

• Drawdown — co to jest obsunięcie kapitału?
• Kiedy sprzedać akcje — sygnały i strategie wyjścia z inwestycji

FAQ

What does the Sharpe Ratio actually measure?

The Sharpe Ratio measures how much excess return a portfolio generates per unit of total volatility, where excess return means return above the risk-free rate. A higher ratio means more return per unit of risk taken — making it a tool for comparing investments with different volatility profiles on a level footing.

What is considered a "good" Sharpe Ratio?

As a rough guide, a Sharpe Ratio below 0.5 is generally seen as weak, 0.5-1.0 as reasonable, 1.0-2.0 as strong, and above 2.0 as exceptional and rarely sustained over long periods. The S&P 500 has historically delivered a long-term Sharpe of around 0.4-0.6, which sets a useful benchmark for equity strategies.

What is the difference between Sharpe and Sortino?

The Sharpe Ratio uses total standard deviation, treating upside and downside volatility equally. The Sortino Ratio only penalizes downside deviation — so it focuses on the risk investors actually care about (losses) and ignores "good" volatility from large gains. Sortino is often more flattering to strategies with rare but large upside spikes.

Why can the Sharpe Ratio be misleading?

It assumes returns follow a normal distribution, but real markets have fat tails — extreme events occur more often than the model predicts. It also depends heavily on the time window, the choice of risk-free rate, and the measurement frequency. Two analysts can compute very different Sharpe ratios for the same strategy depending on these inputs.

Is this financial advice?

No. This article is educational content about a portfolio metric and is not investment advice within the meaning of Polish KNF regulations. Risk-adjusted return metrics are tools, not recommendations — consult a licensed advisor before acting on any portfolio analysis.