The terms filing date and priority date are often used interchangeably, but they are not the same. The filing date is the date when a patent application is first filed at a patent office. The priority date, sometimes called the "effective filing date", is the date used to establish the novelty and/or obviousness of a particular invention relative to other art. The priority date may be earlier than the actual filing date of an application. If an application claims priority to an earlier parent application, then its priority date may be the same as the parent. There are a number of situations where a patent application may claim priority to an earlier application. These include:
- Continuation applications (including continuations, divisionals, and CIPs). A patent application may claim priority to an earlier filed parent application. When this occurs, the priority date of the new application is usually the same as the priority date of the parent application.
- Domestic applications based on foreign or international filings. If a patent application is first filed in a foreign country, or as an international (PCT) application, and then filed domestically (usually within a year the foreign or international filing), then the application that is filed domestically may claim the filing date of the application in the foreign country as its priority date.
- Patent filings based on US provisional patent applications. In the US, an applicant may file a provisional patent application, and then file a full-length application within one year. In this case, the priority date for the full-length application is the date of the provisional application filing.