In Espacenet you can find the priority date in the Bibliographic data section right after the Priority number(s) in the format yyyymmdd. The priority date of a patent is the date on which you first file a patent application in respect of your invention.An element of an international application will be accorded the priority date of the earliest priority application which discloses it. You must supply the complete declaration of priority and the priority document no later than sixteen months after the earliest priority date. What is a patent priority date? Priority date refers to the earliest filing date in a family of patent applications. Filed application for patent filed in the United States may claim the benefit of, or priority to, a prior application filed in the United States. The date of priority counts as the date of filing for both the European application being examined and conflicting European applications under Art. 54(3).