The loan contract number and the IOU number are IOU numbers, which are just an IOU number given by the bank. The loan contract number is a digital number set by the bank according to the loan situation of different users. Moreover, in many cases, what users need to provide is the loan contract number, and the IOU number is generally used internally by the bank and has no specific meaning externally.

Therefore, users need to provide the loan contract number when applying for mortgage tax deduction. If the IOU number is successfully filled in, the user needs to modify it.