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How long does a patent last?
Patent terms are usually 20 years from the date on which the application for patent was filed in the United States. This term may be shortened, however, if the inventor filed an earlier patent application on the same invention. In this case, the patent term will be 20 years from the filing date of the earlier application.
Importantly, protection afforded by a patent does not actually start until the patent is granted (i.e., issued). Thus, the enforceable term of a patent is always shorter than 20 years; exactly how much shorter depends on how long the application was examined in the PTO. For example, if an application is examined in the PTO for five years before it is issued, the enforceable patent term will be only 15 years. Examination periods of five years and more are not uncommon. On the other hand, the patent term can be extended for a limited time under certain circumstances (see "What questions are at issue in current discussions on PTO policy?").
Once a patent has expired, anyone may make, use, offer for sale, sell or import the invention without permission of the patentee.

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