ZIP+4 Code

The ZIP+4 code added a hyphen and four digits to the existing five-digit ZIP Code. The first five numbers continued to identify an area of the country and delivery office to which mail is directed. The sixth and seventh numbers denoted a delivery sector, which may be several blocks, a group of streets, a group of Post Office boxes, several office buildings, a single high-rise office building, a large apartment building or a small geographic area. The last two numbers denoted a delivery segment, which might be one floor of an office building, one side of a street between intersecting streets, specific departments in a firm, or specific Post Office boxes.

On October 1, 1983, the Governors of the Postal Service approved price incentives for First-Class Mail bearing the ZIP+4 Code.