Rule of 72 Calculator
Quickly estimate how many years it takes to double your money at any interest rate, or find the rate needed to double in your target timeframe.
Last updated: Jan 2025Up to date
What is the Rule of 72?
The Rule of 72 is a simple mathematical shortcut that helps you estimate how long it will take for your investment to double in value at a fixed annual rate of return. It's one of the most useful mental math tricks in personal finance.
Formula: Years to Double = 72 ÷ Annual Interest Rate (%)
How to Use the Rule of 72
- Know your return rate: If your FD gives 7% return → 72 ÷ 7 = ~10.3 years to double
- Compare investments: SIP at 12% doubles in 6 years vs FD at 6% doubles in 12 years
- Set goals: Want to double in 5 years? You need 72 ÷ 5 = 14.4% return
- Understand inflation: At 6% inflation, your money's purchasing power halves in 12 years
Rule of 72 Examples in Indian Context
| Investment | Typical Return | Years to Double |
|---|---|---|
| Savings Account | 3-4% | 18-24 years |
| Fixed Deposit | 6-7% | 10-12 years |
| PPF | 7.1% | ~10 years |
| Equity Mutual Funds | 12-15% | 5-6 years |
| Nifty 50 (Historical) | ~12% | 6 years |
Why is it Called Rule of "72"?
The number 72 is used because it has many divisors (1, 2, 3, 4, 6, 8, 9, 12, 18, 24, 36, 72), making mental calculations easy. While 69.3 would be mathematically more accurate (based on natural logarithm of 2), 72 provides a good balance between accuracy and ease of calculation.
Limitations of the Rule of 72
- Most accurate for interest rates between 6% and 10%
- Assumes compound interest with annual compounding
- Doesn't account for taxes on returns
- Assumes constant interest rate over the period
- For rates below 6% or above 10%, use Rule of 69 or Rule of 70 for better accuracy
Related Rules
- Rule of 114: Time to triple your money = 114 ÷ Interest Rate
- Rule of 144: Time to quadruple your money = 144 ÷ Interest Rate
- Rule of 70: More accurate for lower interest rates = 70 ÷ Interest Rate