How fast does your money double? How fast does your debt?
Divide 72 by the interest rate to see roughly how many years it takes to double. It works for savings growing in your favor, and for debt growing against you.
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Hypothetical estimates at a constant rate, with interest added once a year and no payments. Credit cards often compound monthly, so real balances can grow a little faster.
Doubling time at common rates
| Rate | Rule of 72 | Exact | Doublings in 10 years |
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Important disclaimer
This calculator is for general education and information only. It is not financial, investment, tax, legal or insurance advice, and it is not an offer, solicitation or recommendation to buy or sell any product or security.
Results are estimates based only on the numbers you enter. Any growth or return figures are hypothetical, are not guaranteed, and actual returns can be lower or negative. The figures assume a constant rate compounded once a year and ignore taxes, fees, inflation, minimum payments, and changes in rates. Real debt often compounds monthly and may grow faster than shown.
Please consult a licensed financial professional before making financial decisions. Your inputs are processed in your browser and are not saved or sent to NeoPenn Life Strategies LLC.
How is this calculated?
Rule of 72 estimate: years to double ≈ 72 ÷ rate. At 8%, 72 ÷ 8 = 9 years.
In the exact formulas below, write the rate as a decimal: 7% = 0.07.
Exact doubling time (annual compounding): years = ln(2) ÷ ln(1 + rate). At 7%: ln(2) ÷ ln(1.07) ≈ 10.24 years.
Value after N years: amount × (1 + rate)N. Debt assumes no payments are made and interest is added once a year.
Number of doublings: N ÷ exact doubling time. Each doubling multiplies the balance by 2, so 3 doublings means 8× the start.
Work it backwards: 72 ÷ years gives the rate needed to double in that many years. To double in 10 years, you'd need about 7.2% a year.
Make doubling work for you, not against you.
A NeoPenn advisor can help you map out a plan to pay down high-interest debt, build savings, and grow toward retirement with strategies built around your goals and time frame.