A convertible mortgage is an agreement made at the beginning of a term that allows homeowners to change the type of mortgage they hold during its term. If a homeowner wants to start with an open mortgage and then lock into a closed mortgage, a convertible mortgage is the right choice. It offers lower rates than an open mortgage and has the option of switching to a closed term. A conversion to a fixed rate mortgage can also be done by most lenders when the borrower has originally selected a variable rate mortgage and now wishes to move to a fixed rate before the end of the term.