Rule of 72 calculator
Calculator
The calculator needs JavaScript. The tables below give the same numbers for common cases.
How it is worked out
- Rule of 72: years to double ≈ 72 ÷ rate = 72 ÷ 6 = 12.
- Exact: ln 2 ÷ ln(1 + rate) = 11.8957 years.
| Inputs | Answer |
|---|---|
| Annual rate of return: 6 | At 6% a year, money doubles in about 12 years by the rule of 72 (exactly 11.9 years). |
| Annual rate of return: 3 | At 3% a year, money doubles in about 24 years by the rule of 72 (exactly 23.45 years). |
| Annual rate of return: 10 | At 10% a year, money doubles in about 7.2 years by the rule of 72 (exactly 7.27 years). |
How to use it
The rule of 72 estimates the years needed to double money: years ≈ 72 ÷ rate. At 6% that is 12 years. The exact figure is ln 2 ÷ ln(1 + rate), which is 11.9 years at 6%.
The rule works best for rates between about 6% and 10%. The calculator also shows how long it takes to triple. These are estimates from the numbers you type, not financial advice or an offer; real products add fees and change rates.
Frequently asked questions
How long does it take to double money at 6%?
About 12 years by the rule of 72, 11.9 exactly.
Why 72?
It is close to 100 × ln 2 and divides evenly by many common rates.
Does the rule work for inflation?
Yes: at 3% inflation prices double in about 24 years.
Method: standard arithmetic shown step by step; no outside data is used. Checked 2026-11-12.
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General information only. Results are plain arithmetic on the numbers you enter; check anything important (money, health, school work) against your own records or the official source.