How the CAGR calculator works
CAGR stands for Compound Annual Growth Rate. It answers a simple question: "if this investment had grown at a single, steady, compounding rate every year — instead of the bumpy, uneven path it actually took — what would that rate have been?" It's the standard way to compare the performance of two very different investments (say, a stock and a savings account) on an apples-to-apples basis, because it smooths out year-to-year volatility into one clean annualized number.
In "Find CAGR" mode, the formula is CAGR = (Ending Value / Starting Value)^(1 / Years) − 1,
expressed as a percentage. You give the calculator a starting value, an ending value, and the
number of years between them, and it works backward to find the constant annual rate that would
turn one into the other.
In "Project value" mode, the calculator runs the same relationship forward instead of backward —
this is the classic compound interest formula: Ending Value = Starting Value × (1 + rate)^years.
You supply a starting amount, an assumed annual rate, and a number of years, and it tells you
what that starting amount grows into. This mode is useful for forecasting — "if I think this
will grow at 9% a year, what will it be worth in 15 years?" — while "Find CAGR" mode is useful
for looking backward at something that already happened.
Worked example
Find CAGR: Suppose you bought a stock for $10,000 seven years ago, and today it's worth $25,000. Plugging in Starting Value = $10,000, Ending Value = $25,000, and Years = 7 gives:
CAGR = (25,000 / 10,000)^(1/7) − 1 = 2.5^0.142857 − 1 ≈ 13.99%
That means your investment behaved, on average, as if it grew by a steady 13.99% every single year for seven years — even though the real path almost certainly included some up years and some down years along the way.
Project value: Now suppose you're starting fresh with $10,000, you expect a 9% average annual return, and you plan to stay invested for 15 years. Switching to "Project value" mode and entering those numbers gives an ending value of $36,425 — roughly 3.6x your starting amount, purely from letting compounding run for 15 years at 9%.
Why CAGR is not the same as "average return"
A lot of confusion around CAGR comes from mixing it up with the simple (arithmetic) average of a set of yearly returns — the two can tell wildly different stories about the same investment. Here's a stark illustration: suppose a stock gains +50% in year one, then loses −33.3% in year two. The simple average of those two returns is a healthy-looking +8.3%. But walk through the actual dollars: $100 growing 50% becomes $150, and then $150 falling 33.3% drops back to almost exactly $100. Your real compound annual growth rate over those two years is roughly 0% — you ended up right where you started, not up 8.3% a year.
This gap exists because losses and gains are not symmetric in percentage terms — a 33.3% loss fully cancels out a 50% gain, but a naive average doesn't capture that relationship. CAGR (sometimes called the "geometric mean" return) correctly accounts for the compounding path, which is why it's the number that should always be used when evaluating actual investment performance, and the simple average should generally be avoided for anything involving volatility.
Common mistakes to avoid
1. Treating CAGR as "what actually happened every year"
CAGR is a smoothed, hypothetical average — it is not a description of the actual year-by-year journey. A stock with a 14% CAGR over seven years could have crashed 40% in year three and rallied hard in year six; CAGR hides that volatility entirely. Don't assume a high CAGR means a smooth ride, and don't assume next year will look anything like the average.
2. Comparing CAGRs across different time periods without context
A 20% CAGR over 1 year and a 20% CAGR over 10 years are very different achievements — the 10-year figure required sustained performance through multiple market cycles, while the 1-year figure could just be a lucky stretch. Always check the underlying time horizon before comparing two CAGR numbers side by side.
3. Forgetting that "Project value" mode is a forecast, not a fact
The reverse/projection mode is only as good as the rate you assume. Small changes in the assumed annual rate compound into large differences over long horizons — try running the same projection at a conservative rate, your expected rate, and an optimistic rate to see the realistic spread of outcomes, rather than anchoring on a single number.
Using CAGR to compare investments
The real power of CAGR shows up when you use it to compare unlike things on level ground. A savings account paying 4% APY, a stock that went from $10,000 to $25,000 over seven years, and a rental property's appreciation over a decade can all be reduced to a single annualized growth rate and lined up side by side — something that's impossible to do by simply eyeballing raw dollar gains, since each of those examples covers a different time period and starting amount. When you see an investment's CAGR quoted in an annual report, a fund fact sheet, or a stock research site, this is exactly the calculation being described, and now you know exactly how to reproduce it — or check it — yourself.