Methodology and sources
This page explains how area code facts on this site are checked, and where they come from. It is written for readers who want to judge the information rather than take it on trust.
Sources used
The main source is the NANPA Area Code Search tool, published by the North American Numbering Plan Administrator: https://secure.nanpa.com/public-report/npa/search-area-codes. That tool gives, for each code, its state code, its in-service date, its overlay group as shown on that code’s own row, its in-use status, and a single time-zone letter. Where a code’s own row was incomplete for its overlay complex, companion rows and NANPA planning letters were checked before the full group was stated. Planning letters cited on Batch 1 code pages include PL-142, PL-468, PL-563, PL-576, and PL-630, named here by number only, with their full references on the code pages that use them. Region and city lists, and time-zone names, are not given as city lists by the NANPA search tool, which gives a state code and a single letter only. Those fields were therefore taken from corroborated secondary sources that cite NANPA or a state public utility commission, and they are described on code pages as region descriptions, not as NANPA city lists. Where a fact could not be confirmed, it was left out rather than guessed. Examples of facts left out on Batch 1 pages include exact days for some overlay additions and transition dates that no NANPA source stated.
What is checked before a code page is added
A code page is added only when its state, in-service date, overlay group, status, and time-zone letter have been checked, and when it has at least three areas in its region description, a unique history, and a source. Pages that do not meet that bar stay as drafts and are not published. New codes are added in small verified batches, and each batch is checked the same way before its pages are added to the list and by-state directory.
Limits of this method
Area code details can change: new overlays are assigned, boundaries are adjusted, and dialing rules follow those changes. A fact that was correct when checked can therefore become out of date, which is why every code page carries the standard disclaimer and why readers should confirm important details with their carrier or the official NANPA website. This site does not claim to be official, and it does not reproduce the NANPA database itself; it summarises public information for general readers.
Frequently asked questions
Where do the code facts come from?
Core fields come from the NANPA Area Code Search tool, with planning letters where a code’s own row was incomplete. Region descriptions come from corroborated sources, as stated above.
Why are some dates or details missing on a code page?
Because they could not be confirmed from a NANPA source. A missing detail is left out on purpose, rather than filled with a guess.
How often is the information re-checked?
Code pages are re-checked against NANPA sources when new batches are added and when a change is reported. There is no fixed re-check date stated on code pages; the sources section states that the information is based on a recent search of NANPA and official sources.
Sources: NANPA Area Code Search tool: https://secure.nanpa.com/public-report/npa/search-area-codes; NANPA planning letters PL-142, PL-468, PL-563, PL-576, PL-630 (cited on Batch 1 code pages).
Based on a recent search of NANPA and official sources.
This website provides general information about North American area codes, compiled from public sources including NANPA. It is not affiliated with or endorsed by the FCC, NANPA or any telephone carrier. Area code details can change; confirm with your carrier or the official NANPA website. This site does not identify callers or phone owners.