The “Rule of 72” is a quick and easy to remember method for calculating how long it will take your money to double at a given rate.
To do this all you need to do is divide 72 by the rate of return. So if your money is in an investment or account that is earning 8% (I know, that is almost laughable right now) then it will take 9 years for your money to double. Of course this is assuming you allow all interest payments to compound with your original deposit/investment.
72 / 8 = 9
At a 1% rate your money would double in 72 years.
72 / 1 = 72
This is assuming that the rate is fixed and not variable, however, if it is a variable rate you can still make a rough estimate just for kicks by projecting what you think the average rate may be. Of course the lower the interest rate is the longer your investment will take to double, thus the more a variable rate investment will have a chance to fluctuate.