Area Code Guides
Learn what an area code means, what it can (and can’t) tell you about a phone number, and what changes when new codes are added—like overlays, splits, and 10-digit dialing.
How Area Codes Work
Learn the basics of NPAs, the NANP number structure, and why dialing rules change.
Overlay vs Split
Understand the difference between the two most common NPA relief methods and what they mean for 10-digit dialing.
Area Code History
How the NANP grew from 86 area codes in 1947 to more than 800 today, and why splits gave way to overlays.
10-Digit Dialing
Why overlay area codes require all 10 digits for local calls, and which US regions have already made the switch.
About these guides
These articles focus on common questions people search for—what an area code means, why new codes are added, and what changes when an overlay or split is introduced. For the dataset behind this site, see Data Sources.
If you’re looking for a specific code, browse the area codes directory.