How do you determine a patent expiration date (US 7,055,282 B2)?
-- skip to the end for a link to download a term calculator from the USPTO.--
At the Uruguay round of GATT in 1994 the U. S. agreed to change the term of utility and plant applications from 17 years from grant to 20 years from filing. This took effect for applications filed on or after June 8, 1995
However it is more complicated than that. Applications that were in-force on that date or filed before that date get the greater of 17 years from grant and 20 years from filing. Applications filed on or after it get 20 (nominally) years from filing. But what counts as "filing". To determine if an application is pre- or post Uruguay its actual filing date is used. So a continuation application filed June 8th 1995 that fully gets priority from a U.S. non provisonal application filed well before that date, is nonetheless a post-Uruguay application.
An application that is a continuation or divisional application and therefore refers back to claim priority of an earlier application will start its 20 years counting from the earliest application in that chain. A U.S. provisional application or a foreign application isn't included in that chain.
I said that the 20 years is the "nominal" term. The actual term can be affected by many things. One is terminal disclaimer. A terminal disclaimer is used by a patent owner to agree that a patent will automatically terminate when a related patent terminates. This is to prevent so-called "non-statutory double patenting". Also a court can declare a patent invalid or unenforceable and the USPTO can, in a reexamination or other post-grant proceeding,
declare one or all claims as being rejected.
The change from 17 years after issue to 20 years from filing was intended to not make a significant change to the average patent term. If a patent took three years from filing to grant, the actual term would come out about the same under either system. However, it is possible that the patent office might take longer than three years. To compensate for this, utility and plant patents issued from applications filed after May 29, 2000 can have days added on to their term by "patent term adjustment". The number of days the USPTO calculated for this is on the face of the issued patent (note: the USPTO's initial method of calculating this has been challenged in the courts and the USPTO has lost, so the number on the face of the patent may or may not be correct.)
For patents resulting from applications filed between June 8th 1995 and May 29th 2000 there is a different system called "patent term extension" ( not to be confused with an entirely different scheme also called "patent term extention" related to delays through the FDA). Under the non-FDA related PTE, the term of a patent is extended to compensate for delays caused by a secrecy order, an appeal that the patentee won or an interference. This is limited to five years.
To compensate for delays through the FDA processes a patent owner can apply for patent term extension when it gets a go-ahead from the FDA to compensate for the product not being marketable until that process concludes.
The last factor is maintainer fees. All utility patents resulting from applications filed after December 12 1980 require payment of maintenance fees to stay in-force.