How long is a US patent good for?

Answer 1

Utility Patent - 20 years from the date of filing of the earliest application

Design Patent - 14 years from the grant of the patent

Plant Patent - 20 years from the date of filing of the earliest application
http://y12web2.y12.doe.gov/techmgt/lic/patent/tsld007.htm
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Answer 2

Depends on when it was filed, among other things. If the application was filed after June 7, 1995, then it will expire 20 years from the filing date. There's also "patent term adjustment", which means that if the Applicant or the Patent Office causes delay, then days can be added/subtracted from the patent term.