How to calculate patent expiry dates in the United States


Calculating patent expiries for most countries is relatively straightforward. Some countries even calculate it for you and display it in a field in their online databases. Why then, is it so difficult to accurately calculate expiry dates for US patents, and be confident in your answer?

This is a shortened version of a full article which can be accessed at Considerations, concerns and recommendations in calculating patent expiry dates for United States patents, and it’s been some eight years since this article was first written, so it’s natural there will have been some changes made in that time. We’ll look at those later, but first, let’s recap.

The commonly held view of how to calculate US patent expiry dates is as follows:

  • For applications filed prior to, and still in force or pending on, 8 June 1995, the expiry date is the later of 17 years from the issue date, and 20 years from the filing date.
    • For example, US 5219846 has a filing date of 20 December 1991 and an issue date of 15 June 1993. Adding 20 years to the filing date gives 20 December 2011, and adding 17 years to the issue date gives 15 June 2010. The expiry date is the later date, 20 December 2011.
  • For applications filed on or after 8 June 1995, the expiry date is 20 years from the date of the earliest related application, or where there are no earlier applications, the filing date.
    • For example, US 6472448 has a filing date of 27 March 2001. There are no earlier related applications, so adding 20 years to the filing date gives 27 March 2021 as the expiry date.
    • A further example, US 7105503 has a filing date of 15 February 2002, but in this case there are earlier related applications. These are a continuation-in-part, filed on 22 December 2000, of US 6436915, which is a continuation-in-part, filed on 7 April 2000, of US 6214613. The earliest related application has a filing date of 7 April 2000, so adding 20 years gives 7 April 2020 as the expiry date, and not 15 February 2022.

With simple examples such as these you can be confident, but as the number of continuations or continuations-in-part or divisional applications grows it becomes more difficult, and situations where the continuing applications span more than 20 years are particularly troublesome.

Precise details for claiming the benefit of an earlier filed application can be read in the full article Considerations, concerns and recommendations in calculating patent expiry dates for United States patents, but in short, if an applicant wishes for a pending application to have the benefit of the filing date of an earlier filed application, they must make reference to the earlier application. The reference must identify all of the prior applications and indicate the relationship between each application in order to establish codependency throughout the entire chain of prior applications, and usually forms the first paragraph of the specification.

In most cases the earlier filed application upon which the benefit claim is made is also the earliest filed application, and calculation of an expiry date is straightforward as outlined in (2) above, but sometimes it appears that the later application is still “live” even though the expiry date calculation indicates that it should have expired.

For example, take US7477268. This application contains a paragraph that references five earlier filed applications.

The first filed application has a filing date of 20 December 1991. As US7477268 references all earlier filed applications it would be reasonable to say that it is claiming benefit from the first filed application. This would give it an effective filing date of 20 December 1991 and as such an expiry date of 20 December 2011.

Everything is clear up to this point, except when you view the relevant record in the USPTO register, Patent Center, you find that the applicant paid the 4th year maintenance fee on 13 June 2012, which is about 6 months after the “expiry” date. It would appear that the applicant, although having referenced all earlier filed applications in the specification, is not claiming benefit from the first filed application, and there is no indication as to which earlier filed application they are claiming benefit from.

US7477268 finally expired in February 2021, and not because it reached the end of its term, but because the applicant chose not to pay further maintenance fees. At this point, we are a little over 29 years after the first filed application.

We are often told not to rely entirely upon patent term expiry calculators or other indications as to a patent’s status or expiry date, but instead to seek legal advice or confirmation from the relevant national register as this will be the most accurate and up to date information. However, in the case of the USPTO, unless there is a clear indication that a patent has expired or been abandoned, we have to assume that a patent is still current. There is no calculation of the anticipated expiry date, and no clear way of calculating it ourselves.

I understand that many factors come into play here. There are some factors that the USPTO has definitive answers for; factors such as the filing date of the application, patent term adjustments, patent term extensions, terminal disclaimers and statutory disclaimers. Then there appears to be a factor for which the USPTO has no answer; and that is benefit claims. If a clear indication could be made as to the benefit claim, then the rest is easy, and an expiry date calculated. Once we can confidently predict an expiry date then viewing the maintenance fee records in Patent Center will make it clear if a patent is still current.

So, what changes have been made now that some time has passed?

The USPTO has retired PAIR and put Patent Center in its place. It’s easier to access, with a modern layout, and all the old information is still there, and with it, the same old problem of not knowing what the earliest effective filing date is.

The USPTO have published their own tool for calculating patent expiry dates. It’s a spreadsheet, and you enter the filing date, grant date, terminal disclaimers, term adjustment, etc and the expiry is calculated for you. It has a separate section relating to any claim to a domestic benefit, which is a fancy way of asking if there are any continuation or divisional applications.  You need to enter the Earliest Effective Filing Date, which is something we’ve seen before, and something we still do not know, especially when there are two or more earlier applications.

The USPTO now also provide a guide to locating the required information to calculate the patent expiry. It’s on the same page as the new tool above. The document unfortunately still references PAIR, but it only points you to the place where the continuity of the application is listed. It does not assist in choosing the right date.

So, things have changed, yet stayed the same. We’re no closer to determining the earliest effective filing dates, and an easier path to calculating patent expiry dates in the United States.

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