I was reading the JPEG Wikipedia article, and found this quote:

The patent expired in December 2007, but Princeton has sued large numbers of companies for "past infringement" of this patent. (Under U.S. patent laws, a patent owner can sue for "past infringement" up to six years before the filing of a lawsuit, so Princeton could theoretically have continued suing companies until December 2013.)

Does this quote basically says that you cannot sue for software patent infringement after 6 years from the patent expiration date, even if the patent infringement happened while the patent was still not expired?

  • How is this question different from, and not answered by, patents.stackexchange.com/q/19706/18033 ?
    – user18033
    Jul 14, 2018 at 7:48
  • Possible duplicate of Is there a statute of limitation on software patents?
    – user18033
    Jul 14, 2018 at 7:48
  • 1
    @DonQuiKong I do not think the other question I asked was very clear, because the answer I got only say that you only have to pay damages for the recent 6 years of patent infringement, but does not say anything about whether there comes a time where the patent holder is not allowed to sue at all. I asked this question I am asking here in the comments section of that answer, but I was told to make it a separate question, so I did here.
    – user21220
    Jul 14, 2018 at 11:40

1 Answer 1


You can be liable for damages for infringing a patent while it was in force even if the suit commences after the patent has expired. Since damages are only for the most recent six years of infringement, once the patent has been expired for six year there is no point in suing.

  • So if for example a patent holder sued for patent infringement after 4 years from the patent expiration date, will the damages granted to the patent holder only be for the 2 years before the patent expiration date?
    – user21220
    Jul 16, 2018 at 23:20
  • Yes, assuming the infringement was ongoing during those two years. I'm a patent agent and have a lot of expertise and experience in getting patents and in how things work at the USPTO but only an attorney is qualified to give advice about what might happen in court.
    – George White
    Jul 17, 2018 at 0:10

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