Utility patents—the most common kind—expire 20 years after the filing date of the regular formal patent application. This means that the period of time the patent is actually in force will depend on how long it takes the patent to be examined. For instance, if the regular patent application is filed on December 1, 2001, and the patent issues on December 1, 2003, the patent will be in force for 18 years.
Effective June 2000, every patent is guaranteed an in-force period of at least 17 years. The patent term will be extended for as long as necessary to compensate for any of the following:
any delay caused by the PTO failing to examine a new application within 14 months from filing
any delay caused by the PTO failing to take any one of the following actions within four months:
reply to an amendment or to an appeal brief
issue an allowance or office action after a decision on appeal, or
issue a patent after the issue fee is paid and any required drawings are filed
any delay caused by the PTO failing to issue a patent within three years from filing, unless the delay was due to the applicant filing a continuation application or buying a delay to reply to an Office Action, or
any delay due to secrecy orders, appeals, or interferences.
Because the law creating the 20-year patent term became effective June 8, 1995, patents issued prior to that date—or which were pending on that date—will expire 20 years from their filing date or 17 years from their issue date, whichever period is longer. (35 United States Code §154(c)(1).)
Design patents last for 14 years from the date the patent issues, and plant and utility patents last for 20 years from the date of filing.
Izvor:
Patent Copyright & Trademark, 6th Edition
by Stephen Elias and Richard Stim