Why can a good average return still leave you with less than you expected?
A fund reports an average return of 5% a year over the past decade. You invested at the start, so you expect your money to have grown about as much as 5% a year would suggest. Then you check your balance and it’s noticeably lower. The fund isn’t necessarily misleading you. The average just isn’t measuring what you think it is.
Losses need bigger gains to recover
Start with the simplest case. You invest $100, and it rises 50% to $150. The next year it falls 50%, to $75. The average of +50% and −50% is zero, which sounds like breaking even. But you’ve lost a quarter of your money.
It happens because percentages apply to different amounts. The 50% loss came out of a larger balance than the 50% gain was added to. After any loss, you need a larger percentage gain just to get back to where you started. A 20% drop needs a 25% gain to recover; a 50% drop needs 100%.
The same average, different results
Now imagine two investments over 20 years, each starting with $10,000.
The first grows a steady 5% every year. After 20 years, it’s worth $26,533.
The second alternates: up 25% one year, down 15% the next. Its simple average return is also 5% a year. But after 20 years it’s worth $18,335, about $8,200 less. Its actual compounded growth rate is about 3.08% a year.
Both investments could fairly be described as averaging 5%. Only one of them grew like it.
Arithmetic and compound averages
The number that often appears in marketing and conversation is the arithmetic average: add up the yearly returns and divide by the number of years. It describes a typical year.
The number that describes how your money actually grew is the compound annual growth rate, or CAGR. It’s the steady yearly rate that would take you from your starting balance to your ending balance. When returns vary, the CAGR is always lower than the arithmetic average, and the more they swing, the bigger the gap.
That’s why two investments with the same average return can leave very different balances. Volatility isn’t just uncomfortable to live through; it reduces compound growth.
Other reasons your result may differ
Even with the right kind of average, your own experience can differ from a fund’s reported return. Fees reduce what you keep every year. Taxes on dividends and gains reduce it further in taxable accounts. And timing matters: if you added money after a strong run or sold during a downturn, your personal return can be quite different from the fund’s, even though you held the same investment.
What to look at instead
When you’re evaluating an investment or setting expectations, look for the annualized or compound return over a period, which funds report alongside total returns. Look at how much the returns varied from year to year, and at the worst periods, not just the average.
When you plan, use a cautious assumption. If a projection only works at an optimistic return, that’s useful to know before you rely on it.
To see the compound growth rate between two values, use the CAGR calculator. The investment fee calculator shows how much fees take over time, and the compound interest calculator lets you test different return assumptions.
The takeaway
An average return describes a typical year, not your outcome. Ups and downs pull compound growth below the average, and fees, taxes and timing can pull your own result lower still. The compound return is the one that tells you how your money actually grew.
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This article is general education about US personal finance, based on the assumptions and sources described in it. It isn’t financial, tax or legal advice, and examples use hypothetical people and figures.