Rule of 72 Calculator: How Fast Money Doubles
Calculate the return on any investment: total ROI %, profit, annualized CAGR and the doubling time by the rule of 72 next to the exact answer.
Processed entirely in your browser — nothing you enter here is ever uploaded.
Result
About this tool
This page opens the ROI calculator with the doubling-time comparison in front: enter an initial value, a final value and the years between them, and you get the rule-of-72 estimate printed right next to the exact answer.
The rule of 72 is mental arithmetic: divide 72 by the annual growth rate in percent and you get the approximate number of years until the amount doubles — at 8% per year, about 9 years. It is an approximation of ln 2 / ln(1 + r), and it is genuinely accurate only in the middle of the range: between roughly 5% and 12% the error stays within a few percent, while at 1% or at 30% it drifts noticeably.
That honesty is the point of this page: both numbers are always shown side by side, so you can use the shortcut in conversation and still know exactly how far off it is for your rate.
Example. An investment that goes from 200 to 250 shows a 25 percent ROI and a profit of 50.
Limit. CAGR and the rule-of-72 doubling comparison appear only when a positive holding period is supplied, and the starting amount must be greater than zero.