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TimeValue
The classic mental-math shortcut for estimating doubling time — no calculator needed, but here's the precise version.
It's a close approximation of the exact formula ln(2)/ln(1+r), which isn't easy to do in your head. 72 divides evenly by many common rates (6, 8, 9, 12), which is why it stuck as the mental shortcut.
The Rule of 72 is most accurate for rates between about 6% and 10%. Outside that range, the estimate drifts further from the true compound-interest answer — use a compound interest calculator for precision.
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OpenYears to double
9.0 years
72 ÷ 8%
What you entered
Divide 72 by the annual growth rate
72 ÷ 8%= 9.0 yearsResult
Years to double: 9.0 years
At a steady 8% annual return, money roughly doubles every 9.0 years. It's a mental-math shortcut, not exact — for a precise figure use a compound interest calculator instead.