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Quickly calculate how long it takes to double your investment, or find out what interest rate you need to double it within a specific time frame.
1028.6
Years
The Rule of 72 is a quick, useful mental math shortcut used in finance to estimate the number of years it takes to double your money at a given annual fixed interest rate. You simply divide 72 by the annual rate of return.
No, it is an approximation. However, it is remarkably accurate for interest rates between 6% and 10%, which covers most common investment vehicles like FDs, Bonds, and conservative Mutual Funds.
If a Bank FD offers 7% per annum, you do 72 ÷ 7 ≈ 10.2. This means it will take roughly 10 years and 2 months for your principal to double. Alternatively, if a friend says 'I doubled my money in 5 years!', you can verify the required growth: 72 ÷ 5 = 14.4% CAGR.