Sharpe ratio

The Sharpe ratio divides a fund’s return, above a safe risk-free rate, by how much its returns swung around. A higher number means more return for each unit of risk taken.

What it actually measures

Return alone is a half-truth, because a fund can post a big number by taking wild risks. The Sharpe ratio corrects for that. It takes the fund’s return, subtracts what you could have earned risk-free (say from a government security), and divides the result by the fund’s standard deviation, its volatility. So it answers a sharper question than “how much did it make?”: it asks “how much did it make for the stomach-churning it put you through?”

How to use it

Of two funds with a similar return, the one with the higher Sharpe ratio got there with less turbulence, which usually makes it the better-run choice and the easier one to hold. It is most meaningful when comparing funds within the same category, like two large-cap funds, because comparing across very different asset types can mislead.

Its limits

The Sharpe ratio looks backward at past data and is never a promise about the future; a fund’s risk and return can both change. It also treats all volatility as bad, including upside swings, which some argue is unfair. Read it as one useful lens among several, alongside the riskometer and the fund’s mandate, not as a single verdict.