Enter each amount, rate, and time period. The result updates automatically. Review the breakdown to compare the main estimate with the supporting planning figures.
Rule of 72 Calculator
Estimate doubling time from a return rate and compare the shortcut with exact compound growth.
Enter your assumptions
%
$
years
Result
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Rule of 72 estimate
Exact doubling time—
Value at comparison horizon—
Rule-of-72 error—
Rate needed to double in horizon—
Estimated doubling years = 72 ÷ annual rate. Exact years = ln(2) ÷ ln(1 + rate).
What the result means
The main result summarizes the calculation using your current inputs. The supporting figures show the components and useful comparisons.
This estimate is for planning and education. Investment returns, lending terms, taxes, fees, and actual cash flows can differ.
At 8% annual growth, the Rule of 72 estimates 9 years; exact compounding takes about 9.01 years.
What assumptions does this calculator use?
It applies the values shown in the input panel and compounds or amortizes them at the stated interval.
Can I enter decimal values?
Yes. Decimal amounts and rates are supported where they are meaningful.
Are taxes and fees included?
Only when an input explicitly asks for them. Add outside costs separately when planning.
Why might an actual result differ?
Market returns, payment timing, rounding, taxes, and provider rules can change real outcomes.
How should I use the result?
Treat it as a planning estimate, then compare it with statements, quotes, or professional advice.