ZIP+4: The Extended ZIP Code Explained

## What Is ZIP+4?

A ZIP+4 code appends a hyphen and four additional digits to the standard 5-digit ZIP code. For example, **10001-7599** identifies a specific delivery segment within the 10001 ZIP code area.

The USPS introduced ZIP+4 in 1983 to improve automated mail sorting. While the 5-digit code narrows delivery to a post office or zone, the +4 extension narrows it further to a city block face, a building floor, or a cluster of PO Boxes.

## How the +4 Digits Work

| Digits | Meaning |
|--------|---------|
| 6th-7th | Delivery sector (group of streets or buildings) |
| 8th-9th | Delivery segment (block face, floor, or PO Box range) |

For example, in the code 10001-7599:

- **75** = a sector covering a few blocks in Midtown Manhattan
- **99** = a specific segment, perhaps the north side of one street

## Who Uses ZIP+4?

ZIP+4 is not required for personal mail — the USPS will deliver with just the 5-digit code. However, bulk mailers receive **significant postage discounts** (up to 3 cents per piece) when they include the full 9-digit code. This is because ZIP+4 reduces manual sorting steps.

Business uses include:

- **Direct mail campaigns** — CASS-certified address lists with ZIP+4
- **E-commerce shipping** — Faster automated sorting at distribution centers
- **Government filings** — IRS and Census forms require 9-digit codes

## ZIP+4 vs. Delivery Point Barcode">Delivery Point Barcode

The USPS takes precision one step further with the Delivery Point Barcode (DPBC), which adds two more digits to the ZIP+4, creating an 11-digit code that uniquely identifies a single mailbox. The Intelligent Mail Barcode (IMb) now encodes this information along with tracking data.

## Finding Your ZIP+4

You can look up any address's ZIP+4 code using the USPS ZIP Code Lookup tool or third-party address validation services. Most address standardization software automatically appends the +4 extension during CASS processing.