Patent expiration

In the US, priority claimed under 35 U.S.C. 119, 365(a), 365(b), 386(a) or 386(b) is not taken into account in determining the term². So a priority date claimed under these sections, for example from a foreign application, does not start the US 20-year clock².

Some systems allow the term to be lengthened. US patent terms may be extended or adjusted in certain circumstances provided by law¹. Article 63(2) EPC allows a contracting state to extend the term, or grant corresponding protection, for a product or process that must undergo an administrative authorization procedure before it can be put on the market in that state⁷. China's Patent Law provides extensions for unreasonable delay in granting an invention patent and for new pharmaceutical products approved for marketing in China; the drug extension may not exceed five years, and the total effective term may not exceed fourteen years from marketing approval (Article 42)¹⁰.

Patents, and in Europe pending applications, can end before their maximum term if the fees that keep them in force are not paid^1,8,10.

• The invention becomes free to use, subject to other rights. After expiry anyone may make, use, offer for sale, sell or import the invention without permission, as long as the activities are not covered by other unexpired patents¹. So a freedom to operate check still has to consider other patents that remain in force¹.
• Past infringement can still matter. US infringement is defined by acts during the term of the patent⁵. 35 U.S.C. 286 bars recovery for infringement committed more than six years before the complaint or counterclaim is filed⁶. Other limits, such as the marking rule, can also apply¹⁵. See Patented product.
• A revived US patent does not reach things made or used during the lapse. If a maintenance fee is accepted after the grace period, the patent does not affect the right of a person who made, purchased, offered to sell, used or imported something protected by the patent between the end of the grace period and the acceptance, to continue using or selling that specific thing (35 U.S.C. 41(c)(2))³.

1. Find the date the term runs fromFor a US utility patent this is the US filing date, or the earliest filing date of an application specifically referred to under 35 U.S.C. 120, 121, 365(c) or 386(c); priority claimed under 35 U.S.C. 119, 365(a) or (b), or 386(a) or (b) does not count². For a European patent and a Chinese patent it is the filing date^7,10.
2. Apply the maximum termUse the term for the patent type and jurisdiction, for example 20 years for a US utility patent² or 10 years for a Chinese utility model¹⁰.
3. Add any adjustment or extensionUS patent terms may be extended or adjusted in certain circumstances provided by law¹, and China provides term extensions under Article 42¹⁰.
4. Check for a terminal disclaimerA US patent whose term has been disclaimed beyond a specified date cannot have its term adjusted beyond the expiration date specified in the disclaimer (35 U.S.C. 154(b)(2)(B))². For a patent that has received patent term adjustment, the Federal Circuit held in In re Cellect (2023) that obviousness-type double patenting is judged on the expiration date after the adjustment is added, whether or not a terminal disclaimer is required or has been filed¹⁴. See Terminal disclaimer.
5. Check that fees were paidAn unpaid US maintenance fee ends the patent at the end of the 6-month grace period³; an unpaid Chinese annual fee terminates the patent right as of the due date once the 6-month late-payment period has passed^10,13.

The USPTO does not calculate expiration dates for patents. It provides a downloadable patent term calculator to help estimate them¹.