If you deposit money today in an account that pays 4.5% annual interest, how long will it take to double your money? Round your answer to two decimal places. Solution We use the formula: A=P(1+r/100)^n where A=future value($2x) P=present value($x say) r=rate of interest n=time period. 2x=x(1+4.5/100)^n 2=(1.045)^n Taking log on both sides; log 2=n*log(1.045) n=log 2/log(1.045) =15.75 years(Approx)..