How a US phone number is structured
The United States shares one numbering system, the North American Numbering Plan (NANP), with Canada, US territories and a number of Caribbean countries. Every number in it has ten digits after the country code 1:
| Part | Digits | Pattern | Meaning |
|---|---|---|---|
| Area code (NPA) | 3 | NXX | A geographic region, or a special service such as toll-free |
| Exchange (central office code) | 3 | NXX | A block of numbers within the area code, originally tied to a local switch |
| Line number | 4 | XXXX | The individual line |
In the pattern, N means any digit from 2 to 9 and X means any digit from 0 to 9. So neither an area code nor an exchange can start with 0 or 1. A number like (123) 456-7890 can't be a real NANP number.
Special codes: N11, 555, toll-free and 900
N11 codes
Three-digit codes ending in 11 are service codes. They can't be used as area codes or exchanges. The best known is 911 for emergencies. Others include 211 for community services, 311 for non-emergency city services in many places, 411 for directory assistance, 511 for traffic information, 711 for relay services for people who are deaf or hard of hearing, and 811 to have underground utilities marked before digging. The 988 Suicide and Crisis Lifeline is a separate three-digit code launched in July 2022.
555 numbers
The exchange 555 is mostly unassigned. The range 555-0100 through 555-0199 is set aside for fictional use in films, TV and examples, which is why it appears in this page's checker. 555-1212 has long been used for directory assistance. A caller ID showing another 555 number is a strong sign of a fake.
Toll-free codes
800, 833, 844, 855, 866, 877 and 888 are toll-free, meaning the business pays for the call. They aren't tied to a location, and scammers use them too, so a toll-free number proves nothing about who is calling.
900 numbers
Calls to 900 numbers can carry premium charges. Most phone plans allow you to block them.
Area codes that look American but are international
Because Caribbean countries in the NANP use the same ten-digit format, some numbers look like US numbers but are international. Examples include 242 (Bahamas), 246 (Barbados), 284 (British Virgin Islands), 473 (Grenada), 649 (Turks and Caicos), 809, 829 and 849 (Dominican Republic), and 876 and 658 (Jamaica). Calls to them may be billed at international rates. They're common in one-ring scams. US territories such as Puerto Rico (787, 939), the US Virgin Islands (340) and Guam (671) are generally billed like domestic calls on most US plans, but check your own plan.
Overlays and ten-digit dialing
When a region runs out of numbers, a new area code is usually added as an overlay covering the same area. Neighbors can then have different area codes, and everyone has to dial all ten digits for local calls. Ten-digit dialing also became necessary in many more areas around 2021 to make way for 988.
Does an area code show where the caller is?
An area code shows where a number was first assigned. People keep their numbers when they move or switch carriers, and internet numbers can be chosen from almost any code, so the area code tells you about the number's history and little about where the caller is now. For more on what a number does reveal, see how reverse lookup works.
Area code questions
Is 876 a US area code?
No. 876 belongs to Jamaica, which shares the North American Numbering Plan. Calls to it may be billed at international rates.
Can a real phone number use the 555 exchange?
Most 555 numbers aren't assigned to subscribers. 555-0100 to 555-0199 is reserved for fictional use, and 555-1212 has long been used for directory assistance.
Why do I have to dial ten digits for local calls?
Overlay area codes mean neighbors can have different codes, and ten-digit dialing spread to many more areas around 2021 to make way for 988.