Volatility

Volatility measures how much an investment's returns typically deviate from its average return over a given period, most commonly expressed as an annualized standard deviation. A highly volatile asset, like an individual growth stock or emerging market equities, can swing sharply both up and down from month to month. A low-volatility asset, like short-term Treasury bonds, tends to move in a much narrower range.

Volatility is often used as a proxy for risk, since a more volatile portfolio is more likely to experience a large drawdown at an inconvenient time, such as right before a planned withdrawal in retirement. Diversifying across asset classes that don't move in lockstep — stocks, bonds, gold, real estate — is one of the main tools investors use to reduce overall portfolio volatility without necessarily sacrificing long-run return, since the assets' individual ups and downs can partially offset one another.

It's important to remember that volatility measures the size of swings in both directions, not just downside risk — which is why metrics like Max Drawdown and Sortino Ratio are often examined alongside it for a fuller risk picture.