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I am trying to determine when US Patent Number 5,720,421 will expire. Since it was pending before June 8, 1995, I would assume that it has a term of 17 years from the filing date and will be valid until Feb. 24th, 2015. However, it is a Continuation-in-part of Ser. No. 202,513 from Feb. 28, 1994 that was abandoned and I am not sure if this affects the term of the patent. Please help me if you can.

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If you look at the patent rules regarding term you will see that for patents from applications that were pre-Uruguay Round both the new and the old calculation for term are done and the patent gets the longer of the two. The fact that it is a CIP of an earlier application does affect the 20-year from filing calculation. For that, the clock starts at the earliest U.S. priority date (not including provisional applications). So one calculation is 20 years from Feb. 28 1994 and the other is 17 years from Feb. 24 1998. Looks like it is Feb. 24, 2015. Another factor may be a terminal disclaimer. That can cut term short; in order to check that you need the file history. Also, according to the USPTO PAIR database this has two patented children: 5808465 and 5868296. The '296 issued in 1999.

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