The full balance of a mortgage loan may be accelerated and called due (i.e. requiring repayment in full) upon sale or other conveyance of the property that is used to secure the promissory note. This is known as the "due on sale clause". The lender has the right, but not the obligation, to call the note due under this circumstance. In the U.S. virtually all mortgage loans contain these clauses (as oppossed to assumable mortgages which allow transfer of ownership without such acceleration).