GLOSSARY
ZIP+4
By Justin Winter · Updated August 28, 2026
The 4-digit extension USPS adds to a 5-digit ZIP code to identify a specific delivery segment — often a single building, floor, or even a large mail recipient.
The four digits after the hyphen in a ZIP+4 code narrow a ZIP code down to something as small as one side of a street block, a single large building, or a specific delivery route segment, letting automated equipment sort mail more precisely than the base ZIP code alone allows.
It is assigned by USPS address-matching software rather than chosen by the mailer, which is why a correctly typed address without one still gets standardized to include it before mail is printed.
See also
- ZIP Code — The 5-digit number USPS assigns to a geographic delivery area, used to route mail to the right regional and local sorting facility.
- Address standardization — Rewriting an address into the exact form USPS uses — canonical abbreviations, directionals, unit designators, and ZIP+4.
- Delivery Point Validation — A USPS check that confirms an address is a real, individually deliverable delivery point — down to the apartment or suite.
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