Rule of 72 Calculator How long will it take your money to double? A math formula to determine how long it will take to double your money for or against you. For example, if interest is 6%, money will be doubled every 12 years because 72 (Rule of 72) divided by 6 (interest rate) equals 12. Einstein said compound interest was the most powerful force he had ever witnessed. Now you know why. General Information Assumed interest rate:     Income Tax Information   Federal tax rate: 15% 28% 31% 36% 39.6% Specified Rate State and Local tax rate: 0%1%2%3%4%5%6%7%8%9%10%11%12%13%14%15% Specified Rate Combined tax rate: Years it will take your money to double: Taxable Tax Deferred Years to Double   12.5 9.5 6.5 3.5 0.5 0  Taxable      Tax Deferred The accuracy of this calculator and its applicability to your circumstances is not guaranteed. You should obtain personal advice from qualified professionals.