Rule of 72 — Quick Doubling Time Calculator
Calculate how long it takes your money to double using the Rule of 72. A simple formula every investor should know for quick mental math.
The Rule of 72 is the most useful mental math shortcut in finance: divide 72 by your annual return rate to find how many years it takes your money to double. At 12% returns: 72/12 = 6 years to double. At 8%: 72/8 = 9 years. At 6%: 72/6 = 12 years. This simple formula works surprisingly accurately for returns between 4-20% and helps you quickly evaluate any investment opportunity without a calculator.
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Key Information
| Parameter | Details |
|---|---|
| Rule of 72 Formula | 72 / Annual Return = Years to Double |
| At 6% Return | 12 years to double |
| At 12% Return | 6 years to double |
| At 15% Return | 4.8 years to double |
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Use Calculator NowFrequently Asked Questions
How long to double money at 7%?
Using the Rule of 72: 72 / 7 = 10.3 years. The exact mathematical answer is 10.24 years showing the rule accuracy. At 7% your Rs 1 lakh becomes Rs 2 lakh in about 10 years Rs 4 lakh in 20 years and Rs 8 lakh in 30 years. Each doubling period adds the same absolute amount as all previous growth combined — this is the power of compound interest.
How many times does money double in 30 years?
At 12% returns (SIP in equity mutual funds): money doubles every 6 years. In 30 years: 5 doublings = 2^5 = 32x. Rs 1 lakh becomes Rs 32 lakh. At 15% returns: doubles every 4.8 years. In 30 years: 6.25 doublings = approximately 66x. At 7% (PPF rate): doubles every 10.3 years. In 30 years: 2.9 doublings = approximately 7.6x.
What return do I need to double in 5 years?
Using Rule of 72: 72 / 5 = 14.4% annual return needed. This is achievable through equity mutual funds which have historically returned 12-15% CAGR in India over 5+ year periods. In FDs at 7% your money takes 10.3 years to double — more than twice as long. This dramatic difference is why equity investing is essential for wealth creation despite the short-term volatility.
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Last updated: March 2026