The expiration date of a patent, important for purposes of licensing

Expiry of a patent is a matter that is sometimes difficult to determine. Normally, a patent has a life of 20 years from filing.

Therefore, if a patent was filed on 27th September 1988, the patent would normally expire 20 years from this date.

However, the term may be extended for a number of reasons including extreme delays in government approvals outside the Patent Office. This is an unusual situation but is commonin pharmaceuticals and other branches of healthcare where FDA approval can sometimes eat up most of the patent term before the drug can be brought to market.

For a list of patent with term extensions, view the patent and trademark office’s extended term list.

Alternatively, some patents may have a shorter life due to their terms being limited by the terms of an earlier issued patent, by something called a ‘terminal disclaimer’, which is where two patents have been filed which claim essentially the same invention.

Even when issued a patent may expire early for a number of reasons.

If the maintenance fees are not paid, the patent expires at the end of the surcharge period. However, the caveat to this is that expired patents may be revived up to 24 months after they expire, so long as the failure to pay the fee was unintentional. If the expiration date was more than two years in the past, the patent cannot be revived.

If there has been any reexamination or voluntary disclaimer which resulted in a loss of some or all of the claim scope. This should be noted on a certificate attached to the patent image on the USPTO database, usually as the last page in the image file. It is possible that an issued patent can be withdrawn from issue on the order of the Commissioner of Patents.

A patent can also be declared invalid by a court.

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