Exact doubling time of an investment. The Doubling Time Calculator takes annual growth or interest rate and returns exact doubling time plus rule of 72 estimate, time to quadruple. Results update as you type, and the formula is shown under the result so you can repeat it in your own spreadsheet.
Investment maths is about comparing money at different points in time on a fair basis. Compound rates, discounting and annualised returns let you compare options of different sizes and durations. Use the worked example below to check the maths against your own figures.
How the Doubling Time Calculator works
The exact formula for how long compounding takes to double a value. The rule of 72 (72 ÷ rate) is a close mental shortcut for rates between 5% and 12%.
Worked example
With the example values (annual growth or interest rate of 8%), the exact doubling time is 9.0 years; rule of 72 estimate 9.0 years, time to quadruple 18.0 years. Change any figure above and the result updates immediately; use Copy results to paste the summary into a note or email.
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Frequently Asked Questions
How is exact doubling time calculated?
doubling time = ln 2 ÷ ln (1 + rate).
Which figures do I need?
Annual growth or interest rate. Take them from the same period and the same set of accounts or reports so the ratio is consistent, and check the example values as a guide to the units expected.
Does the calculator account for taxes and fees?
Only where there is an input for them. For a true net return, add fees and taxes to your inputs or use the stock and crypto profit calculators, which include them.
