All tools · Finance calculators
Estimate years to double your money at a given rate.
Free to use, no sign-up required. Rule of 72 is one of 198 tools built into Xenition, alongside a chat that can use them for you.
Gives a quick estimate of how long money takes to double at a fixed yearly return, without a calculator or a formula sheet. It works just as well for how fast inflation halves buying power.
Years to double = 72 ÷ annual rate. Years to quadruple = 2 × that. It is a shortcut for the exact figure, ln 2 ÷ ln(1 + rate), and it assumes the return compounds once a year at a steady rate.
At 6% a year, 72 ÷ 6 = 12 years to double and 24 years to quadruple. The exact doubling time at 6% is 11.9 years, so the shortcut is off by about a month.
Very close between roughly 6% and 10%. At 8% it gives 9 years against an exact 9.01. It drifts at very low or very high rates; at 1% or 30% the error grows noticeably.
The exact constant for continuous compounding is about 69.3. 72 is used because it is close and divides evenly by 2, 3, 4, 6, 8, 9 and 12, which makes mental maths easy.
You do not have to open Rule of 72 to use it. Ask Xenition in plain language and it runs the right tool, then carries the answer into whatever you are working on — a document, a spreadsheet, a deck.