Online Calculators since 2009
The Rule of 72 is used to estimate how long it will take an investment to double.
The actual equation is R x T = 72, where R is the interest rate and T is Time, or periods of time, in months or years
From this equation the required interest rate and number of payment periods can be extracted.
This calculator also shows how the figures actually calculate over the time period if an amount is entered.
There is an option to add the results to a table for comparison. A PDF document can be produced from these details
(The table appears the first time you click the "Add to Table" button)
R = Interest rate as a percentage
T = Time Periods
R x T = 72
T = 72 / R
R = 72 / T
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