The formula
is the starting value, the ending value and the number of years.
Where it comes from
ROI is the total percentage change: how much you gained, relative to what you put in. It ignores time, so a 65% gain over 5 years and over 20 years look the same.
CAGR answers a better question: what steady yearly growth rate would turn into over years? Steady growth at rate multiplies the value by each year:
Divide by , then take the -th root of both sides:
Real investments go up and down. CAGR smooths that out into the one rate that would have landed in the same place.
Worked example
$10,000 grows to $16,500 over 5 years:
Note that 65% ÷ 5 = 13% overstates the yearly return. Compounding means each year’s growth builds on the last.
Watch out for
- Deposits and withdrawals. CAGR assumes nothing was added or taken out. If you contributed along the way, the result will overstate your return.
- Volatility hides. Two investments with the same CAGR can have had very different rides.
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