Savings Calculators
Rule of 72 Calculator
Estimate how long money takes to double at a given rate, and the rate needed to double within a set period.
Years to double
10.3 years
- Exact doubling time
- 10.2 years
- Rate needed for your target
- 7.18%
- Value when doubled
- $50,000
How this calculator works
Years ≈ 72 ÷ rate
- 72
- an approximation that works well for rates between 4% and 12%
Example calculation
Illustrative example — not advice
Worked example — the rule of 72 calculator as it loads, using the default figures below.
- 01Enter annual return: 7%.
- 02Enter target doubling period: 10 years.
- 03Enter starting amount: $25,000.
- 04Read the years to double from the results panel: 10.3 years.
Years to double: 10.3 years. Exact doubling time: 10.2 years. Rate needed for your target: 7.18%. Value when doubled: $50,000.
These figures come straight from the calculator above running on the values listed, so you can retype them and confirm every number yourself. Change any input and the results update immediately. Illustrative only — not a quote, offer or recommendation.
Important considerations
- The rule is an approximation — the exact figure uses logarithms.
- It applies equally to debt, which is why high-rate borrowing compounds so quickly.
Related calculators
- Compound Interest CalculatorProject the growth of a balance with compounding and regular contributions.
- Investment CalculatorProjected value of contributions and returns over time.
- Simple Interest CalculatorInterest charged on the original amount only.
- Inflation CalculatorPurchasing power of a sum over time.
- Savings Goal CalculatorMonthly saving needed to hit a target.
- Emergency Fund CalculatorEmergency fund target and time to build it.
Terms used here
Frequently asked questions
How accurate is it?
Within a few months for typical investment returns, drifting at very high or very low rates.
Disclaimer
Legamoney calculators are educational tools. Results are estimates based on the figures you enter and do not constitute financial, tax or legal advice.
Last reviewed 2026-08-01