Why are ZIP+4 codes used?
In 1983, the Postal Service began using an expanded ZIP Code called “ZIP+4.” A ZIP+4 code consists of the original 5-digit ZIP Code plus a 4-digit add-on code. The 4-digit add-on number identifies a geographic segment within the 5-digit delivery area, such as a city block, office building, individual high-volume receiver of mail, or any other unit that would aid efficient mail sorting and delivery. Use of the 4-digit add-on is not mandatory, but it helps the Postal Service direct mail more efficiently and accurately because it reduces handling and significantly decreases the potential for human error and possibility of misdelivery. It also will lead to better control over USPS costs and, in turn, postage rate stability. ZIP+4 is intended for use primarily by business mailers who prepare their mail with typewritten, machine-printed, or computerized addressing formats that can be read by the Postal Service’s automated scanners during processing. Mailers who qualify receive a rate discoun
