Patent applications filed with the USPTO are given a serial or application number in the format of XX/YYY,YYY. The first two digits before the slash (the “XX”) are the series code and the six digits after the slash (the “YYY,YYY”) are the serial or application number. The USPTO added the first series code, fittingly “1”, to patent application serial numbers in 1915.

Different series codes are used for different types of patent applications (e.g., utility application) and proceedings (e.g., ex parte reexamination).  The following chart provides the series code(s) that correspond to each type of patent application or proceeding.

Click here to view the table.

Patent application serial numbers are generally assigned chronologically.  For provisional applications, utility applications, design applications, and reissue applications, the series code also provides information about the year in which an application was filed. For example, utility patent applications having series code “13” were most likely filed in 2012, 2013, or 2014. The USPTO notes, however, that there are some applications for which the serial number and filing date may not fall within the time period you would expect, so it is not a perfect system.

For a list of years when certain series codes were used, check out the USPTO’s Table of Filing Years and Patent Application Serial Numbers, for Patent Applications Filed Since 1882 — for selected document types.

More information about series codes and application numbers can be found in MPEP 503.