Rule of 72 is an approximation used to estimate the years required to double money at a fixed annual rate.
Small differences in interest rates have massive impacts on doubling time. 12% doubles in 6 years, while 15% takes only 4.8 years.
Use the Rule of 72 to quickly filter investment opportunities based on their growth velocity.
Time to Double
The Rule of 72 is the fastest mental math shortcut in personal finance. Simply divide 72 by your annual interest rate to get the approximate number of years it takes to double your money. Our calculator also works in reverse — enter a target doubling period and instantly see the required annual return.
Whether you're comparing a bank FD at 7%, PPF at 7.1%, equity SIP at 12%, or a real estate deal at 9% — the Rule of 72 lets you compare them all at a glance without a spreadsheet.
The formula is deceptively simple: divide 72 by the annual interest rate. The accuracy is best between 5–15% return rates — which covers most Indian investment options.
Years to Double ≈ 72 ÷ Annual Interest Rate (%)Where:
Using Rule of 72 to instantly compare doubling time:
• Bank FD at 7%: 72 ÷ 7 = 10.3 years to double
• PPF at 7.1%: 72 ÷ 7.1 = 10.1 years to double
• Equity Mutual Fund at 12%: 72 ÷ 12 = 6 years to double
• Real Estate at 9%: 72 ÷ 9 = 8 years to double
Conclusion: Equity can double your money ~4 years faster than FD — a massive difference over 30 years!
At a glance — how fast different instruments double your money:
| Investment | Typical Return | Years to Double (Rule of 72) | Risk Level |
|---|---|---|---|
| Savings Account | 3-4% | 18-24 years | Negligible |
| Bank FD | 6.5-7.5% | 9.6-11 years | Very Low |
| PPF | 7.1% | ~10 years | Zero (Govt backed) |
| Debt Mutual Fund | 7-8% | 9-10 years | Low |
| Real Estate | 8-10% | 7.2-9 years | Medium |
| Equity MF (Large Cap) | 10-12% | 6-7.2 years | Medium-High |
| Equity MF (Mid/Small Cap) | 12-15% | 4.8-6 years | High |
The figures provided by this calculator are estimates based on the inputs you provide and standard financial formulas. STOCKCALC.IN does not offer investment advice. Please consult a qualified financial advisor before making any investment decisions.
Verified Contributor
I verified this calculation against the **April 2026 Fiscal Cycle**. If you have questions about the logic, reach out via the Author Page.