What is the due-on-sale clause and how does it affect you, the real estate agent in the current market? The due-on-sale clause (or acceleration clause) is the clause contained in most mortgages that requires the borrower to pay the mortgage loan in full upon sale of the property and is the reason that most real estate related loans are not “assumable.” It gives the lender the right to call the loan due and payable in full when the property is sold.