Rule of 72 Calculator
Estimate how long an investment takes to double using the Rule of 72.
Doubling time in your head
The Rule of 72 is a beautifully simple shortcut: divide 72 by an annual growth rate, and you get roughly the number of years for money to double. This applies it, so you can gauge doubling time instantly — a genuinely handy mental tool for thinking about growth.
Enter a growth rate to see the approximate doubling time.
Why it works, and its uses
The rule is an approximation of the compound-growth maths that happens to be accurate enough for typical rates and easy to do in your head — at 8% money doubles in about nine years, at 6% about twelve. It flips around too: it shows how corrosive inflation or a fee is, since the same rule tells you how fast prices double or how quickly a percentage drag halves your purchasing power. It is not exact, drifting a little at very high or low rates, but as a quick sense-check of what a growth or inflation rate really means over time, it is one of the most useful pieces of financial mental arithmetic there is.
Common questions
How does the Rule of 72 work?
Divide 72 by the annual growth rate to get the approximate years to double — at 8%, about nine years.
Is it exact?
No — it is a close approximation that works well for typical rates and drifts a little at very high or low ones, but it is excellent for quick mental estimates.
Is anything uploaded?
No. The calculation happens in your browser.