What is a confirmation number in a patent application?

This page is an FAQ based on guidance from the Manual of Patent Examining Procedure. It is provided as guidance, with links to the ground truth sources. This is information only: it is not legal advice.

A confirmation number is a four-digit number assigned to each newly filed patent application. It is used in combination with the application number to verify the accuracy of the application number on correspondence filed with the USPTO. This helps avoid misidentification due to transposition errors.

The MPEP states: ‘The confirmation number is a four-digit number that is assigned to each newly filed application. The confirmation number, in combination with the application number, is used to verify the accuracy of the application number placed on correspondence filed with the Office to avoid misidentification of an application due to a transposition error in the application number.’ (MPEP 503)