What is the significance of the effective date on an ex parte reexamination certificate?

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 effective date on an ex parte reexamination certificate is significant for several reasons:

• It marks the date when the certificate becomes legally effective
• It determines when the changes to the patent claims take effect
• It impacts the enforcement of patent rights for the modified claims

MPEP 2290 states: “The certificate is titled ‘Ex Parte Reexamination Certificate.’ The title is followed by the patent number of the original patent and the effective date of the certificate.”

The effective date is crucial for determining the scope of patent protection and for calculating any potential damages in infringement cases involving the reexamined patent.