Rule of 72 Calculator
How long money takes to double.
Enter your values
Enter the annual return in %.
Enter the starting amount in $.
Results update instantly as you type — no submit needed. Your values are remembered on this device, and the shareable link reopens the calculator with exactly these numbers.
- Years to double (rule of 72)
- 9
- Exact years
- 9.01
- Value after doubling
- $20,000.00
- Value in 20 years
- $46,609.57
- Doublings in 30 years
- 3.33
Quick answer
Divide 72 by the annual return to approximate the years needed to double your money.
Years to double ≈ 72 ÷ Rate
At a glance
| What it does | How long money takes to double. |
|---|---|
| Category | Finance |
| Inputs needed | Annual return, Starting amount |
| Main output | Years to double (rule of 72) |
| Formula | Years to double ≈ 72 ÷ Rate |
| Cost | Free — no sign-up, no download |
How to use the Rule of 72 Calculator
- 1Enter your expected annual return.
- 2Optionally enter a starting amount.
- 3Compare the shortcut to the exact answer.
Inputs explained
- Annual return(%)
- Enter the annual return in %.
- Starting amount($)
- Enter the starting amount in $.
Worked example
Using the values the calculator loads with:
Inputs
- Annual return8 %
- Starting amount10000 $
Results
- Years to double (rule of 72)9
- Exact years9.01
- Value after doubling$20,000.00
- Value in 20 years$46,609.57
- Doublings in 30 years3.33
Frequently asked questions
Why 72?
It divides cleanly and closely matches the logarithmic answer for rates between 6% and 10%.
When is it inaccurate?
At very high or very low rates — use 69.3 for continuous compounding.
What do I need to enter into the Rule of 72 Calculator?
Just 2 values: annual return, starting amount. Every field starts with a realistic example, so you can change one number at a time and watch the result update instantly.
How does the Rule of 72 Calculator work out the answer?
Divide 72 by the annual return to approximate the years needed to double your money. It applies the formula Years to double ≈ 72 ÷ Rate and shows the working so you can check each step by hand.
Is the Rule of 72 Calculator free, and do I need an account?
It is completely free with no sign-up, no download and no usage limit. Everything is calculated in your browser, so the numbers you type never leave your device.
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.