Sharpe Ratio Calculator
Calculate the Sharpe ratio to measure risk-adjusted portfolio returns.
What this calculator does
The Sharpe ratio, devised by William Sharpe in 1966, exists because raw returns say nothing about what was risked to achieve them. It divides excess return — the return above the risk-free rate — by the standard deviation of those returns.
What comes out is return per unit of risk. A portfolio delivering 20 percent with violent swings may be a worse holding than one delivering 12 percent steadily, because the second demands far less tolerance for drawdown and is far easier to hold through a poor year without capitulating.
When to use it
The ratio is most useful comparing strategies or funds with genuinely different volatility, where a straight return comparison would mislead. It is also the standard test of whether a manager's outperformance reflects skill or simply more risk than the benchmark carried.
It matters especially where gearing is involved. Leverage turns almost any positive-return strategy into a high-return strategy but barely shifts the Sharpe ratio, since numerator and denominator scale together. That makes it a useful filter against returns that are really just borrowed money at work.
Understanding the inputs
Portfolio return should be the annualised figure over your measurement period, net of all platform and fund charges — gross returns produce a Sharpe ratio that nobody actually received. The risk-free rate should be a gilt yield matched to the same horizon.
Standard deviation is annualised volatility. Computing from monthly returns, take the monthly standard deviation and multiply by the square root of twelve. Use at least three years of data and preferably five or more, since shorter windows give ratios driven by chance rather than by any durable property.
How is this calculated?
Sharpe Ratio = (Portfolio Return − Risk-Free Rate) / Standard Deviation
A worked example
Portfolio A returned 8.4 percent a year with a standard deviation of 14 percent. Against a risk-free rate of 4.5 percent, the excess return is 3.9 percent and the Sharpe ratio is 0.28.
Portfolio B returned 6.1 percent with a standard deviation of 7 percent. Its excess return of 1.6 percent divided by 7 gives 0.23. A is the more efficient of the two despite B's smoother ride — and both sit below the 1.0 mark, which is entirely normal for real multi-asset portfolios.
Limitations and assumptions
Standard deviation counts upside and downside movement equally and assumes normally distributed returns, which markets routinely contradict — large moves occur far more often than the model allows. Strategies carrying hidden tail risk can post outstanding Sharpe ratios for years before failing severely.
The measure is backward-looking, and past returns do not predict future ones. It reveals nothing about maximum drawdown, liquidity, or embedded gearing, and the calculator assumes a flat return with no volatility in its projections. Nothing here is investment advice or a personal recommendation.
Common Questions
- What does the Sharpe ratio measure?
- Return earned above the risk-free rate per unit of volatility taken. Portfolio return minus risk-free rate, divided by standard deviation. It tests whether a strong return came from genuine efficiency or simply from holding something that moved around a great deal in both directions.
- What is a good Sharpe ratio?
- Broadly, under 1.0 is unremarkable, 1.0 to 2.0 is good, over 2.0 is excellent, and over 3.0 warrants scepticism about how the numbers were produced. For perspective, broad equity indices have long-run Sharpe ratios around 0.4 to 0.5, so high figures are rarer than the scale suggests.
- Which risk-free rate applies in the UK?
- A gilt yield matched to your measurement horizon, or the SONIA-linked short rate for short periods. The choice moves the answer more than people expect — when Bank Rate sat near zero, every portfolio's Sharpe ratio looked better than it does now that cash pays meaningfully more.
- Why is standard deviation an imperfect risk measure?
- Because it treats upside movement as identically undesirable to downside. A fund that occasionally rises 15 percent scores as risky as one that occasionally falls 15 percent. It also assumes a normal distribution, which materially understates how often markets produce extreme moves in either direction.
- What is the Sortino ratio?
- A refinement dividing excess return by downside deviation alone, disregarding upside volatility. For strategies with asymmetric returns it gives a fairer reading. A fund with a modest Sharpe but a strong Sortino is one whose volatility largely occurs in the direction investors are happy about.
- Can the ratio be manipulated?
- Easily. Selling out-of-the-money options generates steady small gains and a superb Sharpe ratio until a tail event wipes out years of them. Illiquid holdings valued infrequently show artificially smooth returns for the same reason. An exceptional Sharpe over a short record should prompt questions, not enthusiasm.
- Do fund fees affect the Sharpe ratio?
- They should, and you must use net-of-fee returns for the figure to mean anything. Fees reduce the numerator without touching the denominator, so a 1 percent annual charge on a portfolio with 12 percent volatility knocks roughly 0.08 off the Sharpe ratio — significant when typical values sit below 1.0.
- Can the Sharpe ratio be negative?
- Yes, whenever the portfolio returned less than cash. A negative ratio means you accepted volatility and were paid less than a short-dated gilt for doing so. The size of a negative ratio is not very informative, though, since greater volatility makes it less negative, which is clearly perverse.
- Should I use it to choose funds?
- As one input, over a long window. Across three years or less it is largely noise. It also cannot compare across asset classes on its own — a gilt fund and an equity fund with similar Sharpe ratios are not substitutes, because their absolute return levels are entirely different.