How long until your money doubles? This doubling time calculator tells you how many periods it takes for a quantity to double given a constant growth rate.
Doubling Time Calculator
Using the doubling time calculator
Enter your expected Rate per period as a percentage. The calculator instantly shows how many periods it takes to double.
The period can be whatever timeframe matches your rate: if you enter an annual return, you get years; monthly return, months.
The doubling time formula
The formula for doubling time is:
Where r is the rate per period as a decimal (e.g., 7% = 0.07).
Example: doubling at 7%
How long to double an investment growing at 7% per year?
The Rule of 72
The Rule of 72 is a mental math shortcut for doubling time:
At 8%, money doubles in roughly 72 / 8 = 9 years. At 6%, about 72 / 6 = 12 years. It's surprisingly accurate for rates between 5-15%.
Why 72? It's close to ln(2) × 100 ≈ 69.3, but 72 is easier to divide mentally (it has factors 2, 3, 4, 6, 8, 9, 12...).
Negative rates
If you enter a negative rate, the calculator tells you how many periods ago the amount was twice as high, assuming constant decline. A -5% rate shows -13.51 periods – meaning 13.51 periods in the past.
