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.

How area codes are determined and assigned

A new area code is usually planned by NANPA, the North American Numbering Plan Administrator, and decided by the state's utility regulator. NANPA forecasts when an area code will run out of prefixes and works out options with the carriers. The regulator chooses the form of relief and the dates, under FCC rules, and NANPA assigns the code itself.

The process runs in this order:

1. Forecast. Each area code has 792 prefixes that can be handed out, and each prefix holds 10,000 numbers. Carriers report the numbers they use and expect to need, normally twice a year, and NANPA combines those reports with its own assignment records to publish exhaust projections for each area code every April and October.
2. Notice. When an area code is expected to run out of prefixes within 36 months, NANPA notifies the state commission and the industry.
3. Industry plan. NANPA and the carriers meet, work out options that fit FCC and state rules, and try to agree on one. The plan goes to the state commission with the industry's recommendation, or with the planning results if they can't agree.
4. State decision. The commission decides whether relief is a split, an overlay or a boundary realignment, where any new boundaries fall, when each change takes effect and how the public is told. In a split, it also decides which side keeps the existing code.
5. Planning letter. NANPA publishes a planning letter setting out the approved plan, its dialing rules and its dates. It includes a test number in the new code, working before the code's first numbers go into service, so businesses can check that their phone systems reach it.

The same FCC rule sets two limits. An overlay can't start until ten-digit dialing is mandatory for every call within and between the codes in its area. And an overlay's numbers must go to carriers first-come, first-served, whatever service they provide; a code reserved for one kind of service, such as mobile phones, needs express FCC authority. If prefixes run out faster than forecast and there isn't time to bring in a new code, NANPA can declare jeopardy and ration the remaining prefixes until relief arrives.

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.

What if your area code isn't three digits?

A US or Canadian area code is always three digits, and it never starts with 0 or 1. So 9, 17, 70, 100 and 1000 are not North American area codes. If you've been given one, it's something else, and the digits usually show what:

Outside North America the rules differ. Many countries use area codes of varying length, so a two-digit code is normal there. This table can't tell you which case yours is. The full number, with any plus sign, will settle it.

What goes in the "area code" box on a form?

The first three digits of that phone number. For (202) 555-0100, enter 202, without the brackets and without a leading 1. "Primary phone area code" and "home area code" mean the same thing for that number. Neither one is asking for your ZIP code, or for the code of the place you live now: a mobile number from another state keeps the code it was issued with. If you have a number from outside North America, look for a separate country code box, because a form built only for US numbers may not accept it.

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.