How is the patent term extension calculated for a reissue patent?

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.

The calculation of the patent term extension for a reissue patent follows a specific rule, as outlined in MPEP § 2766:

“With respect to calculating the amount of extension to which the reissued patent is entitled to receive, so long as the original patent claimed the approved product and the reissued patent claims the approved product, the original patent grant date would be used to calculate the extension to which the reissued patent would be entitled.”

This means that if both the original and reissued patents claim the approved product, the extension calculation is based on the grant date of the original patent, not the reissue date. This ensures continuity in the patent term extension process despite the reissue.