What is the effective date for claims in a reissue 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.

Claims in a reissue application are treated as if they were presented in the original patent for the purpose of evaluating patentability over prior art. The MPEP 1440 states:

“The claims in a reissue application are treated as if they were presented in the patent being reissued for purposes of evaluating patentability over prior art, i.e., as if they had the same effective filing date as the original patent.”

This treatment is based on the principle that a reissue patent replaces the original patent and continues its patent privilege. The effective date for claims in a reissue application is the same as the effective filing date of the original patent, even if the reissue application cannot make a benefit claim under 35 U.S.C. 120 to the original patent.