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Rule of 72 calculator

Compare the rule of 72’s quick doubling estimate with exact annual compound growth.

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Compare the rule of 72’s quick doubling estimate with exact annual compound growth.

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Precision and calculation record
Rounding changes displayed numbers, not the calculation. Text, fractions, matrices and CSV schedules keep their own formatting. Automatic keeps up to 12 significant digits, with money shown to cents where applicable.
Step-by-step calculation
Inputs are substituted below. Each line evaluates the next operation; intermediate values are displayed to 12 significant digits while the calculation uses full precision.
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    Save the current answer, then change an input to compare. This clears when you leave.
    Formula and assumptions
    The rule of 72 is a heuristic, not an identity. The exact comparison assumes a positive constant effective annual rate without contributions or withdrawals. Fixed assumptions only: no taxes, fees, changing returns, guarantees or product eligibility. Amounts share one currency.
    Automatic precision shows numbers to 12 significant digits. Thousands separators such as 1,000 are accepted; use a dot for decimals.
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    Use +, −, ×, ÷, parentheses and %. A percentage is divided by 100. This does not change the main tool.
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    Updated 
    Using Rule of 72 calculator
    Compare the rule of 72’s quick doubling estimate with exact annual compound growth.
    The rule of 72 is a heuristic, not an identity. The exact comparison assumes a positive constant effective annual rate without contributions or withdrawals. Fixed assumptions only: no taxes, fees, changing returns, guarantees or product eligibility. Amounts share one currency.
    Next: Compound interest calculator
    A worked example
    Example inputs: annual growth rate (%) = 6. Approximate doubling years = 12.
    Before you use the result
    The rule of 72 is a heuristic, not an identity. The exact comparison assumes a positive constant effective annual rate without contributions or withdrawals. Fixed assumptions only: no taxes, fees, changing returns, guarantees or product eligibility. Amounts share one currency.
    Example results for annual growth rate (%)
    These examples use the formula above. They are reference calculations, not recommended settings.
    Annual growth rate (%)Approximate doubling years
    324
    612
    126
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    ToolOctopus. “Rule of 72 calculator.” Updated 2026-09-26. https://tooloctopus.com/rule-of-72-calculator.
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