What Is the NANP? Simple Explanation

The North American Numbering Plan (NANP) is the shared telephone numbering system used across the United States, Canada, and around twenty Caribbean and North Atlantic nations and territories. It is the reason a phone number in New York, Toronto, and Jamaica all follow the same format and share the country code +1.

How the NANP is structured

Every NANP number has ten digits in a fixed pattern: NPA-NXX-XXXX.

• NPA — the three-digit area code (the geographic region).
• NXX — the three-digit exchange, or central-office code.
• XXXX — the four-digit line number.

See NPA-NXX for a full breakdown of how those digits are assigned. All NANP calls are reached internationally by dialing the +1 country code first.

Which countries the NANP covers

The plan spans more than twenty countries and territories, including the United States, Canada, and many Caribbean nations such as the Bahamas, Jamaica, the Dominican Republic, Barbados, and Trinidad and Tobago, plus U.S. territories like Puerto Rico, Guam, and the U.S. Virgin Islands. Each gets its own area codes within the shared +1 system.

How it is administered

The NANP is overseen by an administrator (NANPA) that assigns new area codes and exchange codes as regions run low on numbers. When an area code fills up, the plan adds capacity — most often through an overlay area code layered over the same region, which is why so many U.S. cities now require 10-digit dialing.

Why the NANP matters

Because the format is shared, any business can get a local-looking number in any NANP region without a physical office there. A virtual phone number in a target city’s area code reads as local to customers. Browse every U.S. code in the area code directory, and note that number portability lets you carry a NANP number between carriers.