What is a Patent Term?
Twenty years from filing, not from grant: how the term is measured, what lengthens or shortens it, and how to calculate an expiration date.
Definition
A patent term is the period during which a patent is enforceable. A US utility patent expires 20 years from the filing date of the earliest non-provisional US application it claims priority to, subject to maintenance fee payment, patent term adjustment, any patent term extension, and any terminal disclaimer.
Key Facts
- Utility and plant patents: 20 years from the earliest effective US non-provisional filing date (35 U.S.C. § 154)
- Design patents: 15 years from grant for applications filed on or after May 13, 2015; 14 years from grant before that
- Provisional applications: Do not count toward the 20 years
- Foreign priority: A Paris Convention priority date does not start the US clock; the US filing date does. For a PCT national-stage application that date is the PCT international filing date, not the later date of US entry
- Patents filed before June 8, 1995: The longer of 17 years from grant or 20 years from filing
Calculating an Expiration Date
Start with the earliest US non-provisional application in the priority chain, or the PCT international filing date for a national-stage application, and add 20 years. Then:
- Add any patent term adjustment printed on the patent for USPTO delay
- Add any patent term extension granted for FDA regulatory review
- Cap the result at any date set by a terminal disclaimer
- Check that every maintenance fee was paid; a missed fee ends the term early
Because continuations and divisionals inherit the parent's filing date, every member of a US family generally expires on the same day regardless of when each was granted. A continuation filed in year 15 of the family has about five years of life.
Why the Filing Date Rule Matters
Under the pre-1995 grant-based rule, an applicant could keep an application pending for decades and then receive a full 17-year term, the so-called submarine patent. Measuring from filing removed that incentive and is why prosecution delay now costs the applicant real term. It is also why PTA exists: without it, USPTO backlog would silently shorten every patent.
Terms Outside the US
Nearly every Patent Cooperation Treaty member grants a 20-year term from the filing date of the national or regional application, with Paris Convention priority not counted. Supplementary protection certificates in Europe and similar mechanisms in Japan and elsewhere play the role of US patent term extension for pharmaceuticals. Utility models, where available, typically last 6 to 10 years.
Expiration in Portfolio Planning
Remaining term is one of the first filters in any pruning or licensing review: a patent with two years left rarely justifies the 11.5-year maintenance fee unless it is actively asserted. Portfolio management tools compute the adjusted expiration date for every asset so the question is answered once rather than at every fee window.
Frequently Asked Questions
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How long does a US patent last?
A utility patent lasts 20 years from the filing date of the earliest non-provisional US application it claims priority to, provided maintenance fees are paid. A design patent lasts 15 years from the grant date. Patent term adjustment and extension can add time; a terminal disclaimer can cap it.
Does the 20-year term start from the provisional filing date?
No. The term runs from the first non-provisional application. Filing a provisional effectively gives the applicant up to 21 years of protection measured from the provisional date, since the 12-month provisional year is not counted.
When does the term start for a PCT national-stage application?
On the PCT international filing date, which counts as the US filing date under 35 U.S.C. § 363. The 30-month national-stage entry date does not restart the clock, and any earlier Paris Convention priority date is not counted.
Do continuation patents expire at the same time as the parent?
Generally yes. A continuation claims the parent's filing date, so its 20-year term ends on the same day, adjusted only by its own patent term adjustment or any terminal disclaimer.
Can a patent term be extended?
Only in two ways. Patent term adjustment compensates for USPTO examination delay and is calculated automatically. Patent term extension under 35 U.S.C. § 156 compensates for FDA review time and must be applied for within 60 days of regulatory approval.
What happens when a patent expires?
The invention enters the public domain and anyone may practice it. The owner can still sue for infringement that occurred during the term, subject to the six-year limit on past damages under 35 U.S.C. § 286.
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