Mortgage Piggyback Calculator (13a) Two Mortgages Versus One Larger Mortgage Who This Calculator is For: Borrowers trying to decide whether they should take a second mortgage, either to avoid mortgage insurance or to avoid the higher interest rate on a jumbo as opposed to a conforming loan amount. What This Calculator Does:This calculator compares the total cost of a combination first mortgage plus a second mortgage to that of a larger first mortgage on which the borrower pays either mortgage insurance or a higher interest rate, over a specified future period. It also shows the highest rate you can pay on the second to break even.