What Is the Sharpe Ratio?

The Sharpe ratio is a ratio that measures how much excess return a fund produced per unit of risk taken. The 'risk' here is the fluctuation of the fund's price — that is, its volatility — while the excess return is how much more the fund returned than a risk-free investment. The ratio answers a single question: "How much return was earned in exchange for the fluctuation endured?" In that sense Sharpe is a risk-adjusted measure that looks not at bare return but at how much 'turbulence' that return came at.

What does the Sharpe ratio measure? The intuition

Two funds may have delivered the same return over the same period; but if one did so with a calm path and the other with sharp swings, the two are not equal. The Sharpe ratio makes exactly this difference visible: by dividing the return by the fluctuation experienced while producing it, it yields 'return per unit of turbulence.'

The logic is that fluctuation is a cost an investor bears. A fund that produces the same return with less fluctuation reached the same outcome with less turbulence; the Sharpe ratio shows that fund with a higher number. In other words, the ratio compresses return and fluctuation, instead of reading them as two separate columns, into a single figure.

How it is calculated: the components

The formula is plain:

Sharpe ratio = (fund's return − risk-free return) ÷ the fund's volatility

Let us take the three components one by one:

• The fund's return — the return over the period examined.
• The risk-free return — the return obtainable with almost no fluctuation; it is usually taken as the yield of short-term government debt instruments or a reference money-market interest rate. The idea is that an investor can earn some return without taking risk, so what is meaningful is the excess return above that base.
• The fund's volatility — the standard deviation of returns, often in its annualized form. This denominator is what lets the excess return be expressed 'per unit of risk.'

The numerator (return − risk-free return) represents the excess return, and the denominator (volatility) the risk taken. So the ratio reduces, without heavy mathematics, 'how much fluctuation each unit of extra return above the risk-free base was bought with' to a single number.

How to read the Sharpe ratio

The higher the Sharpe ratio, the more excess return was earned per unit of fluctuation taken on. A negative Sharpe indicates that, over the period examined, the fund's return fell below even the risk-free return.

But caution is needed here: a high Sharpe does not mean 'a better fund' or 'buy.' The ratio is a photograph of a past period; it does not show the future outcome and is not a recommendation. Also, only ratios computed over the same period and with the same method can be meaningfully placed side by side. This page does not say which Sharpe level should be preferred; it only explains what the ratio measures.

The limits of the Sharpe ratio

Sharpe is a strong but not flawless measure. Its main limits:

• It is backward-looking. It only summarizes realized return and fluctuation; it contains no forecast of the future.
• It assumes a roughly normal distribution. When returns contain rare but sharp shocks (fat tails), standard deviation can under-represent risk, and Sharpe can look more optimistic than it is.
• It penalizes upside and downside fluctuation equally. Because the denominator is volatility, sharp rises count as 'risk' just like sharp falls. Yet for an investor upside fluctuation is often something desired. (To address this limit, derivative measures such as the Sortino ratio, which use only downside deviation, were developed.)

Comparison with other risk measures

Sharpe is not the only measure of risk, and it gives a more complete picture when read together with the measures beside it:

• Maximum drawdown — the largest loss a fund suffered from a peak down to the following trough. It answers "how far did it fall at the worst moment," whereas Sharpe looks at average fluctuation, not a single worst moment.
• Risk value (1-7) — the integer the SPK assigns by mapping a fund's historical return volatility onto seven bands. It classifies fluctuation only; it does not account for return. Sharpe, by contrast, weighs return and fluctuation together.

The three answer different questions, and substituting one for another misleads. To see different funds' return and fluctuation data side by side, you can use the /fon-karsilastirma and /en-cok-kazandiran-fonlar pages; these pages offer no recommendation, they only display the measures.