Considerations, concerns and recommendations in calculating patent expiry dates for United States patents

• US patent expiry – legal requirements and their interpretation in practice.
• Potential complexities associated with numerous continuation-in-parts explored.
• Concerns about determination of ‘earliest effective filing date’ analyzed.
• Patent term adjustment and terminal disclosures explained.

Calculating United States patent expiries for continuing applications involves determining the earliest effective filing date, and is by no means straightforward, especially for chains of applications stretching over 20 years. The United States Patent and Trademark Office provides many definitive answers to the factors determining an expiry date, but leaves one as a great unknown, the earliest effective filing date. A summary of the requirements for claiming the benefit of an earlier filed application is provided, along with examples highlighting the difficulty experienced.