text: formula for calculating interest? variables known:  initial investment ($2,000) additional monthly investment ($500) yearly interest rate (3.5%)  want to find: balance in n (10) years.  please include formulas and solve with the numbers given as an example. ok sorry i missed the $500  so for the initial $2000 you do this:  fv = pv(1+r) to the nth power where  r = interest rate = 0.035 n = number of periods = 10 pv = present value = 2000  $2821.  now the $500 gets really hard, because it is like getting 120 individual investments of $500 each, each having a different period of investment, with an interest rate of 3.5/12 % per month!   this is a really complex equation. each of the 120 terms is like the first formula.  maybe the second link will help?