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. Each claim is entitled to a priority date, which could be the date of filing of the priority application or the date the complete patent application was filed.The priority date of a patent application or patent is the earliest date that can be regarded as the filing date of the inventive matter in question. The priority date determines whether another patent filing or publicly available document qualifies as prior art against one's patent application. "In order to decide if an event took place before it, the priority date has to be based on some frame of reference," Mr Justice Birss said. The priority date of a patent relates to the earliest filing date from within a family of patent applications. What is a patent priority date? Priority date refers to the earliest filing date in a family of patent applications. The date on which you submitted your application from which priority is being claimed is called the priority date. A claim of priority allows a later filed patent application to have a priority date as of the filing date of an earlier filed application.