Compound interest is calculated using the formula A = P(1+r/n)^n×t Where: A = Total accumulated amount (Principal + Interest) P = Principal amount (initial investment) r = Annual interest rate (as a decimal) n = Number of times interest is compounded per year t = Time the money is invested or borrowed (in years) In your sample A= 1(1+0.1)^200 A = 189.9 Don't know where our differences (factor 10) come from, how did you calculate ?