What is a portable mortgage? It's when you sell your house and buy a new place, but you keep your old home loan. If you’ve locked in a low mortgage rate and want to move, imagine the low-rate mortgage moving with you. The big question about portable mortgages is: Are they too good to be true? Porting a mortgage is a real thing, just not in the U.S. — yet Porting a mortgage allows you to keep your existing loan terms and interest rate when you buy another house, rather than getting a new loan that may hav ...