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ZIP+4

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ZIP+4 Extended US Postal Code

The extended 9-digit US postal code that adds a 4-digit add-on to the standard 5-digit ZIP code, pinpointing a specific delivery segment.

Definition

ZIP+4 is the extended version of the standard US postal ZIP code, adding a 4-digit segment after the familiar 5-digit code to identify a much smaller and more specific delivery area. Where a plain ZIP code like 90210 covers a whole neighborhood or town, the full ZIP+4 form 90210-1234 can narrow that down to a specific side of a street, a single apartment building, or a high-volume mail recipient.

The format was introduced by the USPS to speed up automated mail sorting and is written as the 5-digit ZIP, a hyphen, and the 4-digit add-on. Address-verification systems, shipping platforms, and tools like the US ZIP Validator use the full 9-digit form when they need delivery-point precision rather than just a general area.

Key Things to Know

  • 9 digits total, split 5+4: the base ZIP identifies a broad delivery area, and the 4-digit add-on narrows it to a specific segment within that area.
  • Formatted with a hyphen: the standard display form is 12345-6789, use the ZIP Code Formatter to add or remove that hyphen as needed.
  • Not required for basic delivery: mail addressed with just the 5-digit ZIP still gets delivered; the add-on mainly helps automated sorting, bulk-mail discounts, and address-verification accuracy.
  • Assigned to nearly every US address: the USPS maintains ZIP+4 records for the vast majority of deliverable addresses, even though the extra digits rarely appear on everyday mail.
  • Different from an international postal code: unlike a fixed-length code such as India's PIN Code, the US ZIP+4 system splits geographic and delivery-point information into two separate segments joined by a hyphen.

Related Terms

Check DigitCheck Digit (Identifier Validation)

Frequently Asked Questions

What do the last 4 digits of a ZIP+4 code actually mean?
They narrow the standard 5-digit ZIP code down to a specific delivery segment, which might be one side of a street, a single large building, or even one high-volume mail receiver like a business or government office. The [US ZIP Validator](/us-zip-validator/) can confirm whether a 9-digit code you've been given is structurally valid.
Is a ZIP+4 code required for mail to be delivered?
No, the base 5-digit ZIP code is enough for standard delivery, but the extra 4 digits speed up sorting and can matter for bulk mail discounts or precise address verification in shipping and e-commerce systems. Most everyday mail is addressed with just the 5-digit ZIP.
How is a ZIP+4 code formatted?
It's written as the 5-digit ZIP, a hyphen, then the 4-digit add-on, for example 90210-1234. The [ZIP Code Formatter](/zip-code-formatter/) can insert or strip that hyphen depending on which format a form or database expects.
Can two houses on the same street have different ZIP+4 codes?
Yes, if the street is long enough or split by an odd/even numbering convention, the USPS can assign different 4-digit add-ons to different blocks or sides of the same street even though the base 5-digit ZIP is identical.
Does every US address have a published ZIP+4?
Nearly all do, since the USPS assigns ZIP+4 codes to essentially every deliverable address, but the add-on isn't always printed on mail or known to the person living there, it's more visible in shipping labels, address-verification APIs, and USPS lookup tools than in everyday correspondence.