What Is ZIP+4 and When Should You Use It?

ZIP codes  |  April 6, 2026  |  2 min read

The five-digit ZIP code was introduced in 1963. Twenty years later, in 1983, the Postal Service added four more digits to create ZIP+4. The longer code is written with a hyphen, like 30303-2711, and it narrows delivery down far more than the base code can.

What the extra four digits mean

The first two of the four digits identify a delivery sector, which might be a group of streets, several office buildings or a large apartment complex. The last two digits identify a delivery segment inside that sector, such as one side of a street block, one floor of a building or a single high-volume business.

When ZIP+4 is useful

• Bulk mailers use it to qualify for lower postage rates.
• Businesses that receive a lot of mail get their own ZIP+4 so sorting is faster.
• Address validation tools return it to confirm that an address really exists.

When you can skip it

For personal letters and most online forms, the five-digit ZIP is enough. Mail will still arrive without the last four digits. Many checkout forms accept both formats and store the extra digits only if they are supplied.

How to validate the format

A common pattern accepts either five digits or five digits, a hyphen and four digits. In a regular expression that is ^\d{5}(-\d{4})?$. Do not store ZIP codes as numbers: codes in New England and New Jersey start with zero, and a numeric column silently drops it, turning 02108 into 2108.

Testing with ZIP+4

If your form, CRM or shipping integration handles ZIP+4, test both formats. Our generator has a ZIP+4 option that appends four random digits to a real five-digit ZIP. The extra digits are random, so they are useful for format testing but will not match a real delivery segment.