A patent application is filed on 1 January 1999. The application is published 18 months later on 1 July 2000 and granted on 30 May 2001. The patent is valid until:
1 January 2019; 20 years from the filing date of the application
Why? According to the requirements specified under the TRIPS Agreement, a patent is valid (enforceable) from the grant date until 20-years from the filing date of the application. TRIPS was effected in 1995 in industrialized countries belonging to the WTO, in 2000 for most of the rest of the member countries, and it will enter into effect in 2005 for the least developed member countries. Most countries with existing patent systems already had a 20 year patent term, except for the United States. Patent applications filed in the United States prior to 8 June 1995 were awarded a 17 year patent term from the date of issuance. To determine the term of a patent, the 20 years begin counting from the earliest filing of the patent application. The patent remains valid for the entire time as long as any required maintenance fees are paid.