A patent owner is given a period of protection of its exclusive rights in return for publishing the patent to the public for further improvements. Patent rights last only for a limited period of time, and the right to sue other parties for infringing on the patent is based on this period. Thus, inventors and other patent owners may want to calculate the expiration date of their patent. This will depend on the filing date of their patent application and other factors, as well as a patent type. Patents are classified as utility patents, design patents, or plant patents.

For utility patents, which are the most common patent type, patent protection lasts for 20 years after the filing date of the patent application. If a U.S. patent application took a PCT route, the patent term will be 20 years from the date of its PCT international filing with the World Intellectual Property Office (WIPO). The protection of a design patent will continue for 15 years from its design patent issue date.

The patent duration may be adjusted under the Patent Term Adjustment (PTA) which is a process of extending the term of a U.S. patent. Its intention is to accommodate for delays caused by the USPTO during the prosecution of a U.S. utility or plant patent application. The total PTA is an addition to the 20 year lifespan of the issued U.S. patent. When an applicant fails to respond to the office action within 3 months of mailing of the Office action by the examiner, the patent term will be deducted as much with the applicant delay. The USPTO lists the PTA calculation in U.S. patent certificates.