Find the exact time for an investment to double, using logarithms instead of the Rule of 72 shortcut.
Solves the compound growth formula exactly for the number of years, using natural logarithms.
Years: ln(2) ÷ ln(1 + rate)
How does this differ from the Rule of 72?
The Rule of 72 is a fast mental guess. This gives the exact answer using logarithms — useful when you need accuracy more than a quick mental estimate.