How to calculate amount and interest?

Hi friends! I develope a payroll system. Car product. If customer buy a car in 27.000 usd. Paid 7.000$ left 20.000$. Interest 0.60% = 120$.Everymonth customer comes to pay 1666.66$ amount. 0.60% interest then it will substract from 20.000$ amount and 120$ interest. Means the price and interest getting down.Everymonth customer comes to pay and everymonth amount and interest is down and down untill the last month the price =0.00$ and interest =0%.Customer need to pay under 1 year.I want to gernerate the detail for customer and display it into the datagridview.Means in my datagrid will have 12 rows by starting with the first row untill row 12th like sample bellow.No. Amount interest1 20.000 120..12 0.00 0.00How to generate this detail within the amount presented?Thank you.