Volatility, and What the Number Actually Tells You

Volatility is one number: the standard deviation of daily returns, scaled to a year. Everything else said about it is interpretation. This page gives the arithmetic, then measured figures for real securities so the number means something.

The arithmetic

Take each day's return, find how far each sits from the average, square those distances, average them, take the square root. That is the daily standard deviation. Multiply by the square root of 252 — the number of trading days in a year — and you have annualised volatility.

The √252 step is the part worth understanding. Volatility scales with the square root of time, not with time, because daily moves partly cancel rather than accumulate. A stock with 1% daily volatility is not 252% volatile over a year; it is 1% × √252 ≈ 15.9%. The same rule run backwards says a fund quoted at 16% a year moves about 1% on a typical day.

What the numbers actually look like

Measured over the past year:

The spread is the point. 37.7% against 13.0% is not a small difference in character; it is roughly 2.9 times the daily movement for the same money at risk.

The reading almost everyone gets wrong

Volatility counts moves in both directions. A fund that rises 4% a day for a month is extremely volatile and has lost nobody anything. Standard deviation cannot tell the two apart, which is why it is a measure of uncertainty rather than of danger, and why quoting it as "risk" without qualification is sloppy.

It is also backward-looking by construction. A volatility of 13.0% describes the year just measured. Realised volatility clusters — calm periods follow calm periods and violent ones follow violent ones — so it has some predictive content, but a regime change breaks it precisely when it matters.

Why two things at the same volatility are not the same

Volatility says how far something moves, not what moves it. 29.3% for gold and a similar figure for a single stock describe the same amount of movement driven by completely unrelated things — and that difference is what decides whether holding both reduces risk or merely doubles it.

The number that captures it is correlation, not volatility. Gold's correlation with the S&P 500 is 0.333; long Treasuries sit at 0.265. Both move plenty on their own and neither takes its orders from the stock market. You can look any ticker up in the correlation finder.

Beta is a different question

Beta asks how far something moves when the market moves, and it is built from both numbers: correlation multiplied by the ratio of the two volatilities. NVDA's beta of 1.90 against a volatility of 37.7% says most, but not all, of its movement is the market's amplified.

A high volatility with a low beta — gold is the clean example — means something moves a great deal for reasons of its own. That is the combination worth holding alongside equities, and the combination a single volatility number hides completely.

Using it without fooling yourself

• Compare like with like. Annualised from daily returns is the convention used here and by most data providers. The same security measured from weekly or monthly returns gives a different number, often materially.
• It is not a loss estimate. Returns have fatter tails than the normal distribution, so the "95% of moves fall within two standard deviations" rule understates how often large days happen.
• Position size responds to it. Half the position in something twice as volatile carries roughly the same daily swing in money, which is the entire idea behind volatility-based sizing.

Figures on this page are measured from daily returns over the year to 2026-09-24, across 5,264 liquid US securities, and are rebuilt nightly.

Related: risk-adjusted returns · Correlation finder · Back to all articles