Q: when does this patent expire: https://www.google.com/patents/US6186857

A: I try to provide general answers that would be useful to future users of the web site -- teach them how to fish rather than handing them a fish.

Patent term is more confusing than it should be. Unfortunately, to try to make things fair, the rules have a number of layers.

Old patents had a term of 17 years from when they issued. New rules are that apply to patent applications filed after June 8, 1995 are 20 years from the first non-provisional patent application. So you ignore the filing date of the provisional application (if any) and look to the oldest non-provisional patent application in the chain of priority. Some applications claim priority back to an earlier non-provisional application via a divisional application, continuation application, or continuation-in-part application.

There are several things that can change this default 20 year term

1) Patent Term Adjustment -- These are bonus days added to the end of the term to make up for the Patent Office being slow in doing their job. This is printed on the patent.

2) Patent Term Extension -- There are extra days added to things undergoing certain types of regulatory review such as review of a new drug at the FDA. The thought is that patent days should not tick off the clock while you are not allowed to sell the product.

3) Sometimes two patent applications are deemed similar by the patent office and they tie the end date of the second application to the end date of the first application. This is called a terminal disclaimer and rarely has a huge impact due to the new 20 year rule.

4) The patent owner has the option of disclaiming the rest of the patent term. This rarely happens but could if the patent owner was worried about an antitrust charge from maintaining a blatantly invalid patent.

5) Some patents become toothless as the claims are deemed invalid or unenforceable in litigation.

4) The patent may expire early if the patent owner does not pay a renewal fee by start of years 4, 8, and 12. This fee is called a maintenance fee. You can see the status using Public PAIR

Finally, with respect to design patents that cover the distinctive ornamental appearance filed after May 13, 2015, the term is 15 years from issuance. (No maintenance fees, no Patent term adjustment)

With all of these various factors, it may be wise to consult with a patent attorney before making a business decision based upon the existence of a patent that you think is problematic. It may well be that there is some nuance in the set of required elements that you do not have or do not need so you can avoid the patent. It may well be that the patent claims are too broad and read upon prior art and thus may be invalid.

I hope this answer helps.

Kevin E Flynn

A: July 3, 2017.