North American Numbering Plan (NANP)

The NANP is the telephone numbering plan that uses country code +1 to serve the United States, Canada, Bermuda and many Caribbean nations. It defines area codes and local numbers and how they are assigned and dialed.

The North American Numbering Plan (NANP) is the telephone numbering system that organizes telephone numbers for countries and territories that share the country code +1. It provides a uniform format for addressing phone lines so calls can be routed reliably across national and international exchanges. The plan covers the United States and Canada as well as island states and territories in the Caribbean and nearby regions; see an overview for additional context.

Numbering structure

NANP numbers follow a fixed, ten-digit national format: NPA-NXX-XXXX, usually presented with the country code as +1 NPA NXX XXXX for international use. The parts are:

Country code: +1, shared by all NANP participants.
NPA (area code): three digits that identify a geographic region or service.
NXX (central office): three digits that denote a local exchange within the area code.
Line number: four digits that identify an individual subscriber line.

Historically there were digit restrictions on certain positions to make codes unambiguous, and dialing procedures have evolved so that in many areas ten-digit dialing is now required because of overlays and capacity management.

History and governance

The numbering plan originated in the mid-20th century as telephone networks expanded and needed a consistent national scheme to automate call routing. The plan was designed and implemented under the auspices of the Bell System and later administered by designated numbering authorities. Today resource management and assignment are handled by a central numbering administrator and regulated by national agencies such as the Federal Communications Commission (U.S.) and counterpart bodies in other participating countries. Administrative policies have adapted over time in response to growth in demand, new services and mobile telephony.

Dialing practices, special codes and examples

Within the NANP area, local dialing can be seven or ten digits depending on local policy. Long-distance calls within the plan often use a leading 1 before the ten-digit number. Important service ranges are also defined inside the plan: toll-free numbers often use codes such as 800 and the other 8XX series, while premium-rate services have their own prefixes. Examples: a typical U.S. or Canadian number appears as +1 212 555 1234; Bermuda and several Caribbean participants also use +1 forms—see information about the United States, Canada, Bermuda and the Caribbean for local variations.

Number portability, overlays (multiple area codes serving the same geographic area) and number pooling are tools used to extend capacity. Overlays typically require callers to include the area code for all calls, prompting many jurisdictions to transition to mandatory ten-digit dialing.

Notable features and future considerations

A distinctive characteristic of the NANP is that a single country code covers several sovereign states and territories. This shared arrangement simplifies some types of calling but requires coordination among multiple regulators. Continued pressure on numbering resources from growing device counts and new services has led to conservation measures and administrative changes. While the basic +1 NPA NXX XXXX format remains stable, policy and dialing practices continue to change in order to preserve numbering capacity and to adapt to technological shifts.