What is the difference between a filing date and a priority date?

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:

In many cases, a patent application claims priority to a series of applications. For example, a continuation application may claim priority to a parent utility application, which claims priority to a US provisional application. The new application may then claim priority to the first filed application in the series, which in this case, is the provisional application.

If a patent application is an original, non-provisional patent application, not a continuation application, and not previously filed in another country, its filing date is usually the same as its priority date.

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