423 area code — Chattanooga, TN geographic
The 423 area code covers Chattanooga, Tennessee, Eastern and Central time zone, and dates back to September 11, 1995. The same territory is also served by its overlay code (423/729 complex). Keep in mind the code identifies where the number was registered; the person calling may be elsewhere.
The code currently holds 758 working prefixes, held by 55 different carriers. Of these, 557 are pooled prefixes shared by multiple carriers. Numbers are anchored to 75 rate centers — billing localities that fix where each prefix belongs.
The current NANPA exhaust forecast for the 423/729 complex is 1Q 2081.
Unusually, 423 spans two time zones (Eastern and Central). When returning a call, check which part of Tennessee the prefix belongs to — the difference is a full hour.
Local calls inside 423 are dialed 10D; 1+10 digit dialing permissible at service providers discretion.
Worth noting: 423 is one of the few NANP area codes whose territory spans two time zones.
Use this page to decode where 423 numbers come from — and remember that spoofing means the screen can lie about everything except your own caution.
The code was carved out of 615 (1995). As demand grew it in turn gave rise to 865 (1999), 729 (2025).
Largest localities in 423
| Locality (rate center) | Active prefixes | Also served by |
|---|---|---|
| Chattanooga | 183 | — |
| Johnson City | 67 | — |
| Bristol | 35 | — |
| Cleveland | 32 | — |
| Kingsport | 31 | — |
| Morristown | 28 | — |
| Athens | 22 | — |
| Greeneville | 20 | — |
| La Follette | 16 | — |
| Newport | 15 | — |
FAQ
Why do 729 and 423 cover the same place?
They are overlays: when a code runs low on numbers, a new code is added over the same territory instead of splitting it. The 423/729 complex shares one service area, and local calls are dialed with 10 digits.
Will 423 run out of numbers?
NANPA's current forecast projects exhaust in 1Q 2081 — decades of capacity remain.
Why am I getting spam calls from 423 numbers?
Scammers spoof recognizable area codes so calls look local or familiar. A displayed 423 number does not prove the call originated there — see our guide to spotting spoofed calls.
Where is a 423 number from?
423 is assigned to Chattanooga and surrounding areas of Tennessee in the Eastern and Central time zone. The three digits after the area code (the prefix) narrow it down to a rate center.