What is the duration of a U.S. patent, or in other words when does a
U.S. patent expire? I'm looking at U.S. patent # 4,658,425. The date
of the patent April 14, 1987. The application number is 881,523. The
application was filed on June 30, 1986. The title of the patent is
"MICROPHONE ACTUATION CONTROL SYSTEM SUITABLE FOR TELECONFERENCE
SYSTEMS". The Inventor is: Stepehen D. Julstrom and the Assignee is
Shure Brothers, Inc.

Dear captain987,

The basic answer: A U.S. patent expires 20 years after the application was filed.

In the words of the U.S. Patent and Trademark Office:

"A patent for an invention is the grant of a property right to the
inventor, issued by the United States Patent and Trademark Office.
Generally, the term of a new patent is 20 years from the date on which
the application for the patent was filed in the United States or, in
special cases, from the date an earlier related application was filed,
subject to the payment of maintenance fees."
Source:
http://www.uspto.gov/web/offices/pac/doc/general/index.html#patent

"(T)he term of the patent shall be generally 20 years from the date on
which the application for the patent was filed in the United States
or, if the application contains a specific reference to an earlier
filed application under 35 U.S.C. 120, 121 or 365(c), from the date of
the earliest such application was filed, and subject to the payment of
maintenance fees as provided by law. (...) The term of the patent
shall be generally 20 years from the date on which the application for
the patent was filed in the United States or, if the application
contains a specific reference to an earlier filed application under 35
U.S.C. 120, 121 or 365(c), from the date of the earliest such
application was filed, and subject to the payment of maintenance fees
as provided by law. A maintenance fee is due 3 1/2, 7 1/2 and 11 1/2
years after the original grant for all patents issuing from the
applications filed on and after December 12, 1980. The maintenance fee
must be paid at the stipulated times to maintain the patent in force.
After the patent has expired anyone may make, use, offer for sale, or
sell or import the invention without permission of the patentee,
provided that matter covered by other unexpired patents is not used.
The terms may be extended for certain pharmaceuticals and for certain
circumstances as provided by law."
Source:
http://www.uspto.gov/web/offices/pac/doc/general/index.html#nature

This means that U.S. Patent No. 4,658,425 will expire on 30 June 2006,
provided that no "certain circumstances as provided by law" apply to
this specific patent, which seems not very probable regarding the
nature of the described invention.

Hope this answers your question!
Regards,
Scriptor


Source:
United States Patent and Trademark Office: General Information Concerning Patents
http://www.uspto.gov/web/offices/pac/doc/general/index.html

I'm afraid this answer is incorrect.

US patent terms changed in 1995, and for a patent of this date this
patent the old term continues to apply, namely 17 years from date of
issue (grant).  The patent issued on 04-14-1987, and will therefore
have expired by 04-14-2004.

Patent details can be found on the USPTO PAIR site, at

http://portal.uspto.gov/external/portal

See also Google Answers Question Number 2434.

Michael


Michael

Sorry - I think I was incorrect myself.  This patent falls into the
'transitional provisional' period, wherein the expiry is the latest
of:

1.  17 years from issuance, and
2.  20 years from application date.