Compound Interest Formula

FV=PV(1+i)^N

Annuity Formula

FV=PMT(1+i)((1+i)^N - 1)/i

     where
          PV = present value
          FV = future value
          PMT = payment  per period
          i = interest rate in percent per period
          N = number of periods

Example & demo

          PMT = $200 per month
          i = 15% per year = 1.25% per month = 0.0125
          N = 30 years = 360 months

power = Math.pow((1 + I), n);
p = -( (-P * I * power) / (power - 1) );