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 priority date determines whether another patent filing or publicly available document qualifies as prior art against one's patent application.Ordinarily a patent application must be filed within 12 months of the filing date of the earlier application from which priority is claimed. What is a patent priority date? Priority date refers to the earliest filing date in a family of patent applications. A priority claim is made to an earlierfiled patent application. For example, an Applicant can claim priority in a later-filed patent application. The priority date of all matter (whether claimed or not) in an application is, prima facie, the date of filing of the application. In this case, the priority date for the fulllength application is the date of the provisional application filing.