Normally, utility and plant patents expire 20 years from their filing date, except:

• Patents which were in force on June 8, 1995 expire 20 years from their filing date, or 17 years from the date of grant, whichever is later {if G>8JUN95, F+20, else max(G+17,F+20)}
• Maintenance fees must be paid by the 4th, 8th and 12th anniversaries of grant; patents lapse on the anniversary if the fee is not paid.
• The patent term may be adjusted (PTA) for delays attributable to the patent office.
• A terminal portion of the term may have been disclaimed by the applicant.
• The term may have been extended because of regulatory delays.
• The patent may have been invalidated.
• The patent or some of its claims may have been dedicated to the public or disclaimed.

U.S. Design Patents expire 14 years from their date of grant.