issue the First Office action within 14 months of filing of the application. All other office actions has to be issued within 4 months of receipt of an applicant response. Failing to this condition, type A delay will accounted. Type B - USPTO estimates the normal prosecution period of an application to be 3 years, i.e. between the date of filing of the application and the issue of the patent. If the prosecution exceeds this time, then Type B delay come into place. Type B delay will calculated if no RCE (Request For Continued Examination) is filed Prior to completion of 3-year period. If the first RCE is filed after 3-year period then type B delay will be calculated up to the date of filing of RCE. Type C - This type of delay is calculated in the events of secrecy orders or interferences. Applicant Delay - Applicant delay occurs when the applicant fails to respond to the office action within 3 months of mailing of an office action. Calculation: Type A delay= Date of issuance of office Action -(Date of receipt of applicant response + 4 Months/14 Months) Type B delay=Date of issue of Patent/Date of filing of first RCE - (Date of filing of application + 3 years) Total PTA =Type A+Type B + Type C - Applicant Delay -overlapping delays Foreign filing priority The Patent Cooperation Treaty provides a process for a patent filing to claim the priority date of an earlier foreign patent application. Within one year of filing a patent application in one country, an international patent application (which "designates" certain other countries, by default all contracting states) can be made. This holds the original priority date and starts the 20-year validity clock, while allowing the actual patent application in the designated countries (and the associated expenses) to be deferred an additional 20 months. Such a patent would expire earlier than 20 years after U.S. filing. Reissue and reexamination Even if the scope of a patent is narrowed, neither reissue nor reexamination changes the original expiration date. A reissued or reexamined patent expires on the day the original granted patent would have ordinarily expired. Example: The validity of a patent (filing: January 1, 2000; issue: January 1, 2002; end: January 1, 2020) is challenged. The USPTO issues a Certificate of Reexamination on January 1, 2004. The reexamined patent is in force until January 1, 2020,