Postcodes
ZIP+4 and Extended Postal Codes
Extended postal codes add extra digits to a basic code to narrow delivery to a block or building. Learn the concept and when it is used.
Updated 14 October 2026 · 2 min read
An extended postal code adds extra characters to a basic postcode so that it describes a much smaller delivery area. The best-known example is ZIP+4 in the United States, which appends four digits to the five-digit ZIP code.
The concept
A basic postcode might cover hundreds or thousands of addresses. An extension subdivides that area into smaller groups, such as a city block, a side of a street, a floor of a building or a single large receiver. The postal operator gets more detail from the same address without a person reading it.
How it looks
In ZIP+4, the extension is written after a hyphen, so the whole thing looks like two blocks of digits. Other countries use similar ideas by making the main code longer, or by adding a short suffix. The result is a hierarchy with an extra level, which you can compare in postcode structure explained.
Why operators use it
Extended codes help automated sorting. If a barcode on a letter carries the full code, machines can arrange mail in delivery order and reduce manual handling. Bulk mailers are often encouraged to use the extended code because it makes sorting cheaper for the operator. See how mail sorting uses postcodes.
Is it required?
Usually not. Ordinary senders can write only the basic code, and the item will still be delivered. In an online form, the extended part is normally optional, and the field should still accept the basic format; see postcode formats in online forms.
Finding an extended code
The reliable source is the national postal operator, which publishes lookup tools for its own country. Our guide on how to find a postcode explains the general approach.
Extended code vs exact location
Even a very narrow extended code still describes a delivery group defined by the postal operator. It does not give a map position or a doorway. An exact-location code such as UPCS, which refers to a 3 m by 3 m cell, answers a different question and sits alongside the postal code rather than replacing it. See postcodes and exact-location codes together.
Frequently asked questions
What is ZIP+4?
ZIP+4 is the United States extended code, which adds four digits after the five-digit ZIP code to narrow the delivery area.
Do I have to use the extended code?
Usually it is optional. Mail is generally delivered using the basic code, though the extra digits can help automated sorting.