The rules for calculating patents terms changed when the US implemented policies set forth by the Agreement on Trade Related Aspects of Intellectual Property Rights (TRIPS). Prior to this implementation, the term of a US extended 17 years from the issue date. However, to be consistent with the TRIPS recommendations, the policy in the US changed in 1995. The current patent term is extends 20 years from the earliest filing date instead of 17 years from the issue date.
Rather than retroactively changing the patent terms for patents that were pending or in force prior to the policy change, the US has adopted a scheme in which the patent term is calculated based on the longer of the two possible patent terms (17 years from the issue date, or 20 years from the earliest filing date). This makes the calculation of patent terms for older patents somewhat complicated. June 8, 1995 was the "magic date" when the patent term calculation changed.
In terms of patent term calculations, US patents generally fall into 4 categories. The figure below shows a relative timeline for the calculation of patent terms, with the colored bars corresponding to each of the four categories. The bars represent the the pendency of applications, from the filing of the application to the issue date.
There are a number of other factors that affect the term of the patent in the US, including terminal disclaimers, and patent term adjustments. These factors are not included in our current patent term calculations. See a tutorial about these other factors.
Category 1 (Pink Bar)
Patents that issued prior to or on June 7, 1978 had a term that was 17 years from the issue date. These patents have all expired.
Category 2 (Blue Bar)
Patents that were filed after June 7, 1978 and issued before June 8, 1995. These applications have a term that is the longer of the two following options:
1) 17 years from the issue date of the application, or 2) 20 years from the earliest filing date.The term "earliest filing date" means that if the patent application in question is a continuation or divisional application of an earlier US application (the "parent" application), then the filing date of the "parent" is the earliest filing date and is used for calculating the patent term.
In addition, if the application in question is a US nationalization of a PCT application, than the PCT application filing date is used as the earliest filing date.
If the application of interest claims priority to a provisional patent application, the provisional application filing date is not considered to be the earliest filing date.
If the application is a US nationalization of a PCT application that was first filed in another (foreign) country, the PCT filing date is considered to be the earliest filing date, not the date of the prior foreign filing.
Category 3 (Red Bar)
This category applies to applications that were filed before June 8, 1995 and were pending on June 8, 1995. Applications in Category 3 are subject to exactly the same conditions as Category 2; their patent term is the longer of the two following options: 1) 17 years from the issue date of the application, or 2) 20 years from the earliest filing date.
Category 4 (Blue Bar)
For applications filed on or after June 8, 1995, the patent term is 20 years from the earliest filing date. Eventually, barring future changes in patent term policy, all patents will expire 20 years from their earliest filing date.
(See Examples of US patent term calculations)
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