Mortgage Repayment Calculator UK - Version 1.0 Download your free mortgage repayment calculator with our compliments. Work out how much your mortgage repayments will be every month. Just enter the amount borrowed (capital sum) the length of time you want to take to repay the loan (the term) in years and the prevailing interest rate, and click on the Calculate button. Our free mortgage repayment calculator does the rest. The amortization algorithm calculates your precise monthly payments.