Volatility

Volatility is the standard deviation of returns: how far a price swings around its average over a period. The ASX 200 typically swings 10 to 15 percent in a year, a single stock swings 30 to 50 percent, and a term deposit swings nothing. In 2020 the index fell roughly a third in five weeks, which is what a volatility spike looks like in practice. High volatility historically pairs with higher long-run average returns, which is the risk-versus-return trade-off wearing a statistics name.

The critical distinction is volatility versus risk. Volatility is the price moving while you hold; risk is permanent loss - the company that fails, the scam, the forced sale at the bottom. A diversified index held for two decades has never produced a permanent loss in Australian market history; it has produced several 30-to-50 percent drawdowns on the way. Money needed next year cannot afford the swings, which is why the time horizon decides who can hold volatility and who cannot. Super fund risk labels are built on exactly this distinction.

The measurement is standard deviation: take each year's return, subtract the average, square the deviations, average them, and take the square root. Three years of +10, minus 20 and +15 percent averages 1.7 percent, and the deviations are large enough to produce a volatility of roughly 15.5 percent. Daily volatility is annualised by multiplying by the square root of 252 trading days. Nothing about the calculation requires a statistics degree - it is a spread measurement with a formula.

The compounding effect is the mechanism most people miss. Volatility drag means the compounded return sits below the arithmetic average: roughly 8 percent average with 15 percent volatility compounds closer to 6.9 percent, because the variance halves off the top. A $100,000 balance at a true 6.9 percent for 20 years reaches roughly $379,000; at the advertised 8 percent it would reach roughly $466,000. The gap between those two numbers is the price of the ride.

Diversification is the lever that lowers the number. Combining assets that do not move together reduces portfolio volatility without cutting the expected return proportionally, which is the mathematical case for holding a broad index instead of three favourite stocks. A single-stock portfolio with 40 percent volatility has roughly three times the swing of the index for the same average return. The swing is what triggers the selling; the average is what the selling forfeits.

Every super fund labels its options with a risk band, and every label is a volatility statement. High-growth options swing hardest and historically compound most; cash options swing least and compound least. The behavioural cost sits in between: losses hurt roughly twice as much as equivalent gains feel good, which is why the swings trigger selling at exactly the wrong moments. The drawdown risk calculator and the risk tolerance entry both exist to size the swings against the holder before the market does it for free.

A colleague named Brent (yes, that Brent) sold his entire portfolio in March 2020 when the ASX 200 fell by roughly a third in five weeks. The index bottomed that month and regained its pre-COVID level inside a year; Brent re-entered two years later, having bought the recovery twice. His volatility was survivable; his behaviour was not. The highest-leverage thing most Australians can do is size the allocation so the worst realistic drawdown is survivable, then treat the daily swings as noise.