Rule of 72 Calculator
Any country Currency-neutral arithmetic. Enter figures in your own currency; no country tax rules are applied.
Rule of 72 calculator: how long to double money at any return, the exact figure, the effect of fees and inflation, and the rate you need.
Educational estimate only. Not a lending decision. Your numbers stay in this browser.
Results
How to read this: the verdict describes how much room your numbers leave, not a decision or an offer. Change any input to see how much the result moves.
Investing and retirement guides
These guides explain compounding, contribution projections, retirement targets, inflation, and real returns.
- Compound interest explained
- Investment return with contributions
- Retirement savings target
- Inflation and real returns
For all guide topics, open Guides. For source and estimate boundaries, read Calculation Methodology and Sources and Assumptions.
Assumptions and formula
The rule of 72 divides 72 by the yearly return in percent. The exact doubling time is ln 2 ÷ ln(1 + return) with yearly compounding; the rules of 70 and 69.3 are shown too. A fee is taken off the return, and the real return after inflation is (1 + return − fee) ÷ (1 + inflation) − 1.
Inflation defaults to the latest 12 months of the BLS consumer price index for all urban consumers, August 2025 to August 2026: 334.98 over 323.976, or 3.40%. The rate needed to double in a number of years is 72 ÷ years by the rule and 2^(1/years) − 1 exactly. The table compares the rule with the exact answer from 1% to 20%.
Worked example
At 7% a year the rule of 72 gives 10.3 years and the exact answer is 10.2. With a 1% fund fee it takes 11.9 years, and in today’s money, after 3.40% inflation, 27.9 years. To double in 10 years you need 7.18% a year.
Frequently asked questions
Does the rule of 72 work for inflation?
Yes: 72 divided by the inflation rate is roughly how long prices take to double and cash to lose half its value. At 3.4% that is about 21 years.
What is the rule of 72?
A shortcut for how long money takes to double: divide 72 by the yearly return. At 8% that is 9 years; the exact answer is 9.01 years.
How accurate is the rule of 72?
Within a few weeks for returns of about 5% to 12%. At 1% it says 72 years against an exact 69.7; at 20% it says 3.6 against 3.8. The table on this page shows the gap at each rate.
How do fees change how long it takes to double?
They come straight off the return. At 7% a year money doubles in about 10.2 years; with a 1% fee it takes 11.9.
How long does inflation take to halve my money?
At the 3.40% inflation of the year to August 2026, prices double and the purchasing power of cash halves in about 20.7 years. 72 ÷ 3.4 gives 21.2.
What return do I need to double my money in 10 years?
About 7.2% a year by the rule (72 ÷ 10); exactly 7.18%.
Is this a doubling time calculator?
Yes: a rule of 72 calculator and doubling time calculator that shows how long to double money at any rate, with the exact figure alongside the rule of 72.
What is the rule of 72 equation?
Years to double ≈ 72 ÷ the yearly return in percent. At 6% that is 12 years; the exact equation, ln 2 ÷ ln(1.06), gives 11.9.
Sources
Sources reviewed 4 October 2026: checked against their current editions on that date.
- U.S. Bureau of Labor Statistics, CPI-U: 12-month inflation to August 2026 (334.98 over 323.976).
This page is an educational estimate, not personal financial or tax advice. Eligibility and individual circumstances can change the result.