When Does A Patent Expire?
Most would say 20 years from its effective filing date, unless the USPTO calculated a patent term adjustment. Calculating this date often proves easy: the face of the patent typically shows its earliest effective filing date and the expiration date falls on the 20th anniversary of that filing date. But sometimes it takes a rare fact pattern to make us realize the answer to such a seemingly simple question may not be so simple.
To illustrate, what if a patentee asserted its patent on the 20th anniversary of its effective filing date? Better yet, what if a patentee asserted its patent on the sixth anniversary of the 20th anniversary of its effective filing date? When specifically does the patent expire, and did the patentee file its complaint within the statutory period to seek damages?
Source: JD Supra