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What is a Sharpe Ratio and How to Use it to Compare Funds

Last Updated: 2026-06-27 6 min read

When comparing mutual funds, most investors follow a simple rule: they pick the fund with the highest historical return. If Fund A returned 18% last year and Fund B returned 14%, Fund A is assumed to be the winner.

However, in the stock market, returns never come for free; they are purchased with risk. If Fund A achieved its 18% return by investing in highly volatile small-cap stocks, while Fund B achieved its 14% return by investing in stable large-caps, Fund B might actually be the smarter choice.

To compare funds fairly, we must look at Risk-Adjusted Returns. The most widely used metric for this is the Sharpe Ratio. Developed by Nobel laureate William F. Sharpe, this ratio calculates how much excess return you receive for the extra volatility you endure.

This guide explains the Sharpe Ratio formula, walks through a comparative case study, and shows you how to use it to select the most efficient funds.

1. What is the Sharpe Ratio?

The Sharpe Ratio measures the excess return of an investment portfolio per unit of its volatility (risk).

  • Excess Return: This is the return of the portfolio minus the risk-free rate (the interest rate of safe government bonds). We subtract the risk-free rate because you could have earned that return with zero risk; we only care about the extra returns the manager generated by taking market risks.
  • Volatility: This is measured as the Standard Deviation of the fund’s returns.

The Formula:

Sharpe Ratio =
Rp - Rf σp

Where:

  • Rp = Expected portfolio return
  • Rf = Risk-free interest rate (e.g. government treasury yields)
  • σp = Standard deviation of the portfolio (volatility)

2. Case Study: Comparing Fund X and Fund Y

Let’s see how the Sharpe Ratio helps you choose between two mutual funds. Assume the risk-free interest rate is 6.00%:

  • Fund X: Reports an average return of 15.00%, with a Standard Deviation (volatility) of 10.00%.
  • Fund Y: Reports an average return of 18.00%, with a Standard Deviation (volatility) of 20.00%.

Let’s calculate the Sharpe Ratios:

For Fund X:

Sharpe =
15% - 6% 10%
=
9% 10%
= 0.90

For Fund Y:

Sharpe =
18% - 6% 20%
=
12% 20%
= 0.60

The Verdict:

  • Fund X Sharpe Ratio: 0.90
  • Fund Y Sharpe Ratio: 0.60

Even though Fund Y delivered a higher raw return (18% vs. 15%), Fund X is the superior investment.

Fund X generates 0.90% of excess return for every 1% of volatility it takes on. Fund Y is highly volatile, generating only 0.60% of excess return per unit of risk. To get that extra 3% of return in Fund Y, you had to double your exposure to price swings (SD of 20% vs 10%). Fund X is much more efficient at turning risk into profit.

To compare risk-adjusted metrics against other debt and equity vehicles, check out:

3. How to Use Sharpe Ratio in Fund Selection

  • Higher is Better: A higher Sharpe Ratio indicates that the fund manager is highly skilled at generating outperformance without taking on excessive risk.
    • Sharpe > 1.0: Excellent.
    • Sharpe 0.5 - 1.0: Good/Acceptable.
    • Sharpe < 0.5: Poor. The returns do not justify the risk.
  • Only Compare Within the Same Category: Never compare the Sharpe Ratio of an equity small-cap fund with a short-term debt fund. Debt funds have low volatility, which artificially inflates their Sharpe Ratios. Instead, compare a mid-cap fund’s Sharpe Ratio against other mid-cap funds to identify the most efficient manager.
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