US Area Codes — where they are and how they work

Area code guides by time zone

Each guide is written from the numbering records for that code — NANPA's database and planning letters, and the state regulator's orders — so dates, overlays and dialing rules are sourced rather than copied from other directories.

How US area codes work

US numbers belong to the North American Numbering Plan (NANP), which AT&T developed in 1947 and began implementing in 1951. It is shared by 20 countries — the United States and its territories, Canada, Bermuda and 17 Caribbean countries and territories — under one international country code, 1.

In NANPA's notation, N is any digit from 2 to 9 and X is any digit from 0 to 9, which is why no area code or prefix starts with 0 or 1. When an area runs short of prefixes, regulators have used three approaches:

Overlays are why ten-digit dialing spread. If two neighbours can hold the same seven digits under different area codes, the switch has to be told which one you mean. A second push came from the 988 crisis line: the FCC required 82 area codes that still allowed seven-digit dialing and used 988 as a local prefix to move to ten digits. Arizona's 480 was one of them.

What an area code tells you — and what it doesn't

• It tells you where the number was issued. NANPA's area code database records the state or province each code belongs to.
• It doesn't tell you where the caller is. Mobile numbers keep their code when people move, and internet-based services can assign numbers outside the caller's own area.
• It doesn't prove who is calling. Caller ID can be falsified; the FCC calls this spoofing. Judge an unexpected call on what the caller asks for, not on the code.
• It isn't a country code. "202" or "720" can look like international codes, but they follow the country code 1. The ITU list of country codes shows which one- to three-digit codes belong to other countries.

For businesses, area codes also shape call routing: which numbers a PBX treats as local, how auto-attendants match callers, and what breaks when an overlay arrives. That's covered in our guide to area codes and call routing, and caller-ID delivery across carriers in CLI vs NCLI routes.

About these guides

We add guides a few at a time and check every date against a primary record. Where sources disagree and no primary record settles it, the guide says so. Exhaust projections come from NANPA's April 2026 analysis and will be updated when NANPA publishes new forecasts.