Termination of the enforceability period of a patent at the end of the patent term or for failure to pay a maintenance fee. Patent terms prior to June 5, 1995 were 17 years from the date that the patent application was issued. However, current law measures the term of a patent 20 years from the date that the patent application is filed. Since 2013, design patents last 15 years from the date they are granted.
Under certain circumstances, patent term extension may be granted, typically due to delays by the USPTO or FDA in the approval process.