Rule of 72 Calculator
Enter an annual interest rate to find how long your investment takes to double, or enter a target number of years to find the required rate.
Use the Rule of 72 Calculator
Rule of 72 Calculator
%
Enter any rate between 0.1% and 500%.
years
Enter a target number of years between 0.1 and 200.
Enter a value and click Calculate.
Formula Used
Exact (Compounded)
Doubling Time at Common Rates
| Annual Rate | Rule of 72 (years) | Exact (years) |
|---|
Summary
The Rule of 72 is a quick mental math shortcut used in finance and investing. Divide 72 by an annual interest rate to estimate the number of years it takes for an investment to double in value. You can also reverse it: divide 72 by a target number of years to find the annual rate needed. While not perfectly precise, it is accurate within a few percent for rates between 2% and 30%.
How it works
- Choose a calculation mode: find doubling time from a rate, or find required rate from years.
- Enter the annual interest rate (%) or the target number of years.
- The calculator applies the Rule of 72 formula: Years = 72 / Rate, or Rate = 72 / Years.
- A comparison table shows doubling times for common rates so you can see the context.
- Results update instantly as you type.
Use cases
- Quickly estimate how long a savings account or CD takes to double.
- Compare compounding rates side by side without a spreadsheet.
- Understand the impact of inflation on purchasing power over time.
- Evaluate whether an investment rate meets your financial goals.
- Teach the concept of compound interest in a classroom setting.
- Sanity-check compound interest projections from a financial advisor.
Frequently Asked Questions
Last updated: 2026-05-23 · Reviewed by Nham Vu