Wondering when you can double your dough? This quick trick makes calculations easy. (Although as my former finance professor would be faster to mention, “Katie, this method is an estimate; it’s not completely accurate.”)

You only need one variable: your compounded rate of return (interest rate in your savings account, for example). Divide 72 by this interest rate, and the resulting number shows how many years it’ll take for you to double your money.

Example:
I have $1000 and want to know when I’ll have $2000 without adding a single cent. My interest rate is 5%. Here we go!

72 / 5 = 14.4 years until my money doubles