For most patents (at least the ones I looked at) there is no more than 1 year difference between "Priority Date" and "Filing Date": often exactly 1 year, and if not, just under 1 year.

This must be due to the fact that one has 1 year to do the actual filing after the provisional one.

However, rarely, the delay between "Priority Date" and "Filing Date" is significantly more than 1 year.

How is this legally possible?

  • Can you link a specific example?
    – pbhj
    Jun 29 '17 at 0:05

It is likely you are seeing the effects of a continuation (or divisional, outside of the US). The continuation retains the priority date of its parent, but has a much later filing date.

By way of example:

  • A Canadian application (CA1) is filed on 1 Jun 2012. CA1 therefore has a filing date of 1 Jun 2012, but no priority date.
  • A US application (US1) claiming priority to CA1 is filed on 31 May 2013 (within 12 months of CA1). US1 therefore has a filing date of 31 May 2013, and a priority date of 1 Jun 2012.
  • A US continuation (US2) is filed from US1 on 1 Oct 2016. US2 retains the priority claims of its parent (US1). US2 therefore has a filing date of 1 Oct 2016, and a priority date of 1 Jun 2012.
  • It might be worth to add that in those cases the patent term is not 20 years from the filing date but from the first parents filing date. (/Us patents before they changed from 17 after grant).
    – DonQuiKong
    Jun 29 '17 at 6:57

I assume you mean a difference of years, not days or weeks, but some countries now allow you to miss the 1 year priority date. Details in this Q/A, which discusses a two months grace period some countries give.

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