How to use it
- Enter Annual return %.
The formula
Years to double ≈ 72 ÷ annual return %.
Worked example
About this calculator
The rule of 72 is the fastest way to feel compound growth without a calculator: divide 72 by the return and you have the doubling time. It turns abstract percentages into a timeline — the language in which long-term decisions actually get made.
Its real power is comparison. 6% doubles money in 12 years; 8% in 9; the two extra points of return are 'one extra doubling' over a working lifetime — the honest argument for keeping fees low and starting early.
Frequently asked questions
How accurate is it?
Very good between about 4% and 15%; it drifts at extremes. It's a shortcut, not a substitute for the compound formula.
Is there a rule for tripling?
Yes — divide 115 by the return: at 8%, tripling takes about 14.4 years. We show it in the breakdown.
Does it work for inflation too?
Yes, in reverse: at 6% inflation, prices double (money halves) in about 12 years.
Tips
- Time in the market beats timing the market.
- Reinvest returns to let compounding work.
- Keep fees low — they compound against you.
Key terms
- Compounding
- Earning returns on past returns.
- CAGR
- The smoothed annual growth rate.
- Yield
- Income as a percent of price.