simple interest:
principal x ( 1 + (rate as decimal x number of years))
example if you put 100 dollars in a bank for 5 years at 5% interest at the end of the 5 years you would have:
100 x (1+(0.05 x 5)) = 100 x (1+(0.25)) = 100 x 1.25 = 125 dollars
125-100 = 25 dollars interest
