2.1.7 Standard Deviation

Spread around an average

If a fund has averaged 12% a year with a standard deviation of 15%, that means individual yearly returns have typically ranged well above and below that 12% average, sometimes by a wide margin. A fund with the same 12% average but a standard deviation of only 6% has historically delivered a much steadier, more predictable path to the same long-run number.

Statistically, standard deviation captures how far returns have scattered around their average. A fund with an annualised standard deviation of 12% and an average return of 14% has seen its annual results fall roughly between 2% and 26% about two-thirds of the time. The higher the number, the wider that band of likely outcomes in any single year.

Why two funds with equal returns can feel very different

Standard deviation is the reason two funds can post identical returns over ten years while feeling completely different to hold. The fund with the higher standard deviation likely had sharper falls along the way, testing the investor's patience far more, even though the destination looked the same on paper at the end.

A common misconception is that lower standard deviation is always better. It is not: a liquid fund with almost no volatility also has almost no real return. The goal is adequate return per unit of volatility taken, not minimum volatility. Standard deviation is also the input behind the Sharpe ratio and much of modern portfolio theory, which is why it appears on nearly every fund factsheet over three- and five-year periods.

Using it sensibly

Standard deviation is most useful when comparing funds within the same category, where it can highlight which one has historically taken a rougher path to a similar destination. It says nothing about the direction of future returns, only about how widely past returns have varied, so it should sit alongside other measures rather than being used alone.

The comparison only makes sense within a category. Indian large-cap funds typically show annualised standard deviations of 12-15%, small-cap funds 18-25%, and debt funds far lower at 1-5% depending on duration. Comparing a small-cap fund's volatility to a large-cap fund's is meaningless; comparing two funds in the same category reveals which manager delivered similar returns with a smoother ride, which in turn reduces the chance of a panic-driven exit during a drawdown.