python - Future Value of yearly investments -

suppose have investment plan invest fixed amount @ beginning of every year. compute total value of investment @ end of last year. inputs amount invest each year, interest rate, , number of years of investment.

this program calculates future value of constant yearly investment. enter yearly investment: 200 enter annual interest rate: .06 enter number of years: 12 value in 12 years is: 3576.427533818945

i've tried few different things, below, doesn't give me 3576.42, gives me $400. ideas?

principal = eval(input("enter yearly investment: ")) apr = eval(input("enter annual interest rate: ")) years = eval(input("enter number of years: ")) in range(years):     principal = principal * (1+apr) print("the value in 12 years is: ", principal) 

if it's yearly investment, should add every year:

yearly = float(input("enter yearly investment: ")) apr = float(input("enter annual interest rate: ")) years = int(input("enter number of years: "))  total = 0 in range(years):     total += yearly     total *= 1 + apr  print("the value in 12 years is: ", total) 

with inputs, outputs

('the value in 12 years is: ', 3576.427533818945) 

update: responding questions comments, clarify what's going on:

1) can use int() yearly , same answer, fine if invest whole number of currency. using float works allows amount 199.99, example.

2) += , *= convenient shorthand: total += yearly means total = total + yearly. it's little easier type, more important, more expresses meaning. read this

for in range(years): # each year     total += yearly    # grow total adding yearly investment     total *= 1 + apr   # grow total multiplying (1 + apr) 

the longer form isn't clear:

for in range(years):        # each year     total = total + yearly    # add total , yearly , assign total     total = total * (1 + apr) # multiply total (1 + apr) , assign total