In order to keep a granted patent in force, maintenance fees must be paid at 3.5 years, 7.5 years and 11.5 years from the date when a patent application is issued to a patent with a patent number assigned. If the maintenance fee is not timely paid, that patent will go expired. In specific, if the maintenance fee is not paid within a six month grace period after the payment due, the patent will go expired.

Fortunately, an expired patent can be reinstated if a petition is filed with a petition fee and an unpaid maintenance fee. The fees are not cheap, though.  What is required is to file a petition to revive an unintentionally expired patent together with a petition fee and the missing maintenance fee. It is strongly recommended to file the petition within two years from the date of expiration so as to enjoy an immediate petition grant if filed through the electronic filing system or EFS-WEB. If it is filed via fax or mail, it will take up to six to eight months for a petition examiner to review and issue a petition grant.

In case a petition to revive an expired patent after two years from the expiration date, then an addition statement supporting the fact that the patent expiration was unintentional. It will be tough to beat petition examiners to issue a petition grant if an unintentional expiration of the patent is not thoroughly addressed in the statement with supporting evidence.

Even though you missed the final due of a patent maintenance fee, still you can reinstate the expired patent contrary to common knowledge that there is no way to reinstate a patent expired with missing a timely payment of a patent maintenance fee.