Mortgage Loans and Calculations - show work 12. Calculate the original loan size of a fixed-payment mortgage if the monthly payment is $1700, the annual interest is 5%, and the original loan term is 15 years. Answer: 13. For a loan of $200,000 at 4 percent annual interest for 30 years, find the balance at the end of 4 years and at 15 years, assuming monthly payments. Answer: Answer: b, Balance at end of year 5: Balance at end of year 20: Balance at end of year 30: d