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The University of Massachusetts Amherst


Patent Expiration and Patent Term Adjustment

The term of a patent in the U.S. depends on several factors. The following document is provided to assist you in locating information required for estimating a patent term expiration date:

Other sources of patent term data may exist that are not maintained by the USPTO. One such source is the FDA's Orange Book for Approved Drug Products with Therapeutic Equivalence Evaluations which includes patent expiration dates, some of which may include periods of exclusivity administered by the FDA that add onto patent term. Additional patent term may also be privately granted by an Act of Congress, and court decisions may establish patent expiration dates that are not reflected in USPTO records.

Patent Term Calculator

The USPTO does not calculate expiration dates for patents. In response to patent owner and public inquiry, the USPTO is providing a downloadable patent term calculator as a resource to help the public estimate the expiration date of a patent. The calculator can be used to estimate the expiration dates of utility, plant, or design patents. The calculator contains prompts to enter specific information related to the patent in order to help in estimating expiration dates. This information can be obtained from USPTO's online systems, links to which are provided below.

Maintenance Fees

Maintain your patent

Maintenance fees are required to keep in force all utility and reissue utility patents based on applications filed on or after December 12, 1980. Maintenance fees are not required for a design or plant patent, or for statutory invention registrations.

Maintenance fee status can be checked here:

What if there's a mistake in the patent?

If a typographical, clerical, or other minor error is made by the applicant that is not fixed before the patent issues, the applicant can request a Certificate of Correction to fix the error for a fee. A Certificate of Correction is a document issued by the USPTO detailing the errors made and their location in the patent. That Certificate is affixed to the front of the issued patent in future print copies, and at the end in electronic copies.

More significant errors in a patent may be corrected or amended by:

(A) a reissue of the patent,

(C) a disclaimer, or

(D) reexamination of the patent.

A detailed explanation of each of these processes can be found in Chapter 1400 of the Manual of Patent Examination Procedure on the USPTO website at

Patent Trial and Appeal Board (PTAB)

The USPTO The Patent Trial and Appeal Board (PTAB) is a tribunal within the United States Patent and Trademark Office (USPTO) that review appeals during the application and decides patentability questions for issued patents raised by third parties in trials after the patent issues.

The Board includes statutory members and administrative patent judges. The statutory members of the Board are the USPTO Director, Deputy Director, Commissioner for Patents, and Commissioner for Trademarks.  

Administrative patent judges are appointed by the Secretary of Commerce and are legally and technically trained. Judges have extensive patent legal experience prior to their appointment on the Board, for example, in private practice, in government practice (e.g., at the Department of Justice or the International Trade Commission), and as in-house counsel in companies. Many also have served as USPTO examiners or judicial law clerks.  

The Board also includes patent attorneys, law clerks, and paralegals along with support staff to administer proceedings and hearings.


Management and Maintenance

Information about managing a patent is provided by the USPTO here:, including how patents can be maintained, enforced, transferred, and protected, the owner's patent rights, and how a patent can be infringed. Factors such as patent markings, determining a patent termmaintaining a patent in force, and correcting a patent are also addressed. This section also defines patent ownership and how it can be assigned or licensed.

Post Grant Review

Post grant review is a trial proceeding to review the patentability of one or more claims in a patent brought by a third party filing a petition on or prior to the date that is 9 months after the grant of the patent or issuance of a reissue patent. A post grant review may be instituted upon a showing that it is more likely than not that at least one claim challenged is unpatentable. If the proceeding is instituted and not dismissed, a final determination by the Board will be issued within 1 year (extendable for good cause by 6 months).

Derivation Proceeding

A derivation proceeding is a trial proceeding to determine whether (i) an inventor named in an earlier application derived the claimed invention from an inventor named in the petitioner's application, and (ii) the earlier application claiming such invention was filed without authorization. An applicant subject to the first-inventor-to-file provisions may file a petition to institute a derivation proceeding only within 1 year of the first publication of a claim to an invention that is the same or substantially the same as the earlier application's claim to the invention. The petition must be supported by substantial evidence that the claimed invention was derived from an inventor named in the petitioner's application. 

Inter Partes Review

Inter partes review is a trial proceeding to review the patentability of one or more claims in a patent only on a ground that could be raised under §§ 102 or 103, and only on the basis of prior art consisting of patents or printed publications. For first-inventor-to-file patents, inter partes review process begins with a third party (a person who is not the owner of the patent) filing a petition after the later of either: (1) 9 months after the grant of the patent or issuance of a reissue patent; or (2) if a post grant review is instituted, the termination of the post grant review. These deadlines do not apply to first-to-invent patents. The patent owner may file a preliminary response to the petition. An inter partes review may be instituted upon a showing that there is a reasonable likelihood that the petitioner would prevail with respect to at least one claim challenged. If the proceeding is instituted and not dismissed, a final determination by the Board will be issued within 1 year (extendable for good cause by 6 months). 

Patent Infringement

Patent infringement consists of “unauthorized making, using, offering for sale, or selling any patented invention within the United States, or importing into the United States any patented invention during its term.” You the patent owner may sue in federal court to stop the infringement and ask for financial damages.

Accused infringers may argue that their actions do not constitute infringement. Determining infringement primarily involves comparing the language of the patent claims to an accused product or process. The parties might hire expert witnesses to help the court understand the issues.

Although U.S. patents are presumed valid, a common defense to an accusation of infringement is to argue that the patent in question is invalid. A federal court makes the final decision.