zip4

ZIP4, commonly referred to as ZIP+4, is a four-digit add-on to the United States ZIP code. It was introduced by the United States Postal Service in 1983 to improve mail sorting and delivery accuracy. A standard five-digit ZIP code identifies a broad postal delivery area; the ZIP+4 adds a hyphen and four digits (for example, 10001-2345) to designate a more precise delivery segment within that area.

The additional four digits identify a portion of the delivery route, such as a street, a group of addresses, a single large mailbox, or a PO Box. This level of detail allows mail to be sorted to a more specific location and is used to improve processing efficiency and routing accuracy in automated systems.

ZIP+4 is commonly used to optimize postage, reduce handling time, and improve address verification. For business mailers, providing the ZIP+4 can support finer routing, higher automation discounts, and more accurate delivery tracking. While it can enhance precision, the four-digit suffix is not always required; many mailings are delivered correctly using only the five-digit ZIP code, and the ZIP+4 may be omitted in standard addresses.

ZIP+4 codes are maintained by the USPS and may change as delivery routes are updated. They can be looked up through USPS address tools or licensed data providers and are used in various data applications for routing, shipping, and demographic analysis.