Rule of 72: Estimate How Fast Money Can Double
The Rule of 72 is a mental shortcut for estimating how long money might take to double at a constant annual rate: divide 72 by the percentage rate.
Change the inputs and compare scenarios with the related RetirementMetric calculator.
Open the calculatorQuick examples
At 6%, the shortcut estimates about 12 years; at 8%, about 9 years; at 10%, about 7.2 years.
Where it helps
It is useful for intuition and comparing rates, especially when teaching compounding.
Where it breaks down
Real investments do not deliver a constant return each year. Fees, taxes, contributions and volatility mean actual results can differ substantially.
How to use this number responsibly
Use the result as a planning range rather than a forecast. Re-run the calculation when your balance, contribution rate, debt, retirement date, tax situation or spending target changes. For investment projections, compare multiple return assumptions because future market returns are unknown.
What this calculator does not know
RetirementMetric does not know your complete tax situation, benefits, investment holdings, insurance needs or household expenses. The tools are educational estimates, not individualized investment, tax or legal advice.
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