ZIP+4 Code
An extended 9-digit ZIP code in the format 5+4 that identifies a more precise delivery point, such as a city block, building floor, or individual high-volume receiver.
The USPS introduced ZIP+4 codes in 1983 to provide finer granularity than the basic 5-digit ZIP code. The additional four digits after the hyphen narrow the delivery area from an entire post office zone to a specific segment: one side of a street between two intersections, a single floor in a large office building, a group of PO Boxes, or even an individual high-volume mailer. For example, 10001-2345 identifies a particular set of addresses within midtown Manhattan.
While ZIP+4 codes are not mandatory for mail delivery, they accelerate processing by allowing automated equipment to bypass several sorting steps. The USPS offers postage discounts on bulk mailings that include ZIP+4 codes, making them standard in commercial mail.
ZIP+4 codes change more frequently than 5-digit ZIP codes because they track delivery routes rather than geographic regions. The USPS updates its ZIP+4 file monthly, and mailers who claim automation discounts must use a current version.