What does average annual return actually mean?

There are two ways to average returns and they give different answers. The simple arithmetic average adds the yearly returns and divides by the number of years. The compound annual growth rate, the figure that actually describes what happened to your money, is the single steady rate that would turn your starting balance into your ending balance over that period. When returns vary, the compound figure is always lower, and the gap grows with volatility.

The clearest demonstration is a two-year sequence: up 50 percent, then down 50 percent. The arithmetic average is zero, suggesting you broke even. In reality $100 becomes $150, then loses half to $75, a 25 percent loss, and the compound annual rate is about negative 13 percent. This is why losses hurt disproportionately, a 50 percent decline requires a 100 percent gain just to recover, and why volatility itself is costly rather than merely uncomfortable. When you see an investment advertising an average annual return, the honest question is which average, and a fund quoting arithmetic averages on volatile returns is flattering itself. Regulators require standardized performance reporting for exactly this reason, and comparing total return over a full period is more informative than any annual figure.