Refinancing One FRM Into Two to Lower Net Cost (3c) Who This Calculator is For: Borrowers trying to decide whether refinancing one FRM into two FRMs will lower costs. What This Calculator Does:This calculator compares the total cost of an existing first mortgage on which the borrower may pay mortgage insurance with that of a combination 80% first mortgage plus a second mortgage at a higher rate, over a specified future period. It also shows the highest rate you can pay on the second to break even.