Your ZIP+4 is a basic five-digit code with four digits added as an extra identifier. It helps to identify a geographic segment within the five-digit delivery area, such as a city block, a group of apartments, an individual high-volume receiver of mail, or a post office box.

ZIP codes are a type of postal code used by the U.S. Postal Service to route mail. First introduced by the Post Office Department in 1963, ZIP stands for zone improvement plan, and was initially established to help the USPS deliver packages. Today it is used to ship almost anything to an address.

United States ZIP codes are five numerical digits long. ZIP+4 codes, also known as add-on or plus-four codes, include four additional digits that identify a geographic segment within a ZIP code delivery area.

A United States postal code, for example, might be either five digits or five digits followed a hyphen (dash) and another four digits (12345-1234). If you are validating US postal codes, allow for both conditions. The following rule validates a field that can be five digits, five digits + dash + 4 digits, or blank.