What is the 1003 mortgage application form?The 1003 mortgage application form is the industry standard form used by nearly all mortgage lenders in the United States. This basic form, or its equivalent, must be completed by a borrower to apply for a mortgage. While some lenders may use alternative forms or simply accept basic borrower information about identity, property type and value, the vast majority of lenders rely on the 1003 form. Generally, the 1003 form is completed twice during a mortgage transaction: once during the initial application and once at closing to confirm the terms of the loan. Some lenders allow borrowers to complete the form at home, while others assist borrowers in person or over the phone. In either case, a potential borrower should understand the 1003 format and the information required before completing the form.