What interest rate do you need to double your money in 10 years?
R = 72/t = 72/10 = 7.2% Example Calculation in Months If you invest a sum of money at 0.5% interest per month, how long will it take you to double your investment? t=72/R = 72/0.5 = 144 months (since R is a monthly rate the answer is in months rather than years)
Therefore, since R is a monthly rate the answer is in months rather than years, the interest rate that you need for an $5000 investment compounded annually to double in 10 years is 7.2%