Area code 423: Tennessee
What is area code 423?
Area code 423 is a US state area code for Tennessee, on Eastern Time and Central Time. It has 761 prefixes in service across 75 rate centers, the largest being Chattanooga, Johnson City and Bristol. It shares its area with 729, so local numbers there can start with any of them. Local calls there take 10 digits.
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See the phone add-onArea code 423 facts
| Location | Tennessee, United States |
|---|---|
| Time zones | Eastern Time and Central Time |
| Overlays | 729 |
| Split from | 615 |
| In service since | September 11, 1995 |
| Local calls | 10 digits; toll calls 1 + 10 digits |
| Carrier | Not shown. An area code is where a number was issued; numbers port between carriers. Check line type |
In short: 423 is Tennessee (Eastern Time and Central Time). Format checks here are free and run in your browser; the current carrier and line type need a live lookup. Bulk phone number validator · Pro + Phone plan
Local time in area code 423
America/New_York
America/Chicago
Prefixes in service
761 of 792 possible
75 rate centers
Which cities and towns use area code 423?
NANPA records each prefix against a rate center, the local billing area a number belongs to, usually named after its main town. These are the 423 rate centers with the most prefixes in service. 63 smaller ones aren't listed.
| Rate center | Prefixes |
|---|---|
| Chattanooga | 183 |
| Johnson City | 67 |
| Bristol | 36 |
| Kingsport | 32 |
| Cleveland | 32 |
| Morristown | 28 |
| Athens | 22 |
| Greeneville | 20 |
| La Follette | 16 |
| Newport | 15 |
| Elizabethton | 13 |
| Midway (Sullivan) | 12 |
Source: NANPA central office code assignments, file dated 10/17/2026. Each prefix holds up to 10,000 numbers.
How do I dial a 423 number?
NANPA's dialling plan for 423: local calls inside the code take 10 digits, toll calls 1 + 10 digits. From another area code, dial 1 first. From abroad, use +1. The examples use 555-0147, from a range reserved for fictional numbers.
| Local call inside 423 | 423-555-0147 |
|---|---|
| From another US or Canadian area code | 1-423-555-0147 |
| From outside North America | +1 423 555 0147 |
| E.164, for CRMs and SMS tools | +14235550147 |
When did area code 423 start?
Area code 423 went into service on September 11, 1995, split from 615. Today 423 and 729 cover the same area as an overlay, which is why 10-digit dialling is needed for local calls there.
Tools for 423 numbers
- Bulk phone number validator
Format, country and number type for every number in a CSV, with E.164 output.
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- Area code time zone
Local time for a list of numbers, with a callable-now flag.
- NPA-NXX lookup
Rate center and state for one prefix, a level below the area code.
- TCPA calling hours checker
Whether it's inside the federal 8 a.m. to 9 p.m. calling window there now.
Next step
A 423 number tells you where it was issued, not what it is now.
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Area code 423 questions
- What state is area code 423?
- Area code 423 is in Tennessee, United States. Its largest rate centers by number of prefixes are Chattanooga, Johnson City, Bristol, Kingsport and Cleveland.
- What time zone is area code 423 in?
- Eastern Time and Central Time. The code crosses a time zone line, so the local time depends on where in the area the number was issued.
- What area codes overlay 423?
- 729. An overlay adds a new code to the same area instead of splitting it, so neighbours can have different area codes and local calls need 10 digits.
- When did area code 423 start?
- Area code 423 went into service on September 11, 1995, split from 615.
- Is a 423 number a cell phone or a landline?
- The area code can't tell you. In the US and Canada mobiles, landlines and VoIP lines share area codes and prefixes, and numbers move between carriers and line types. Only a live line-type lookup answers it for one number.
- How many phone numbers does area code 423 have?
- 761 of its 792 possible prefixes are in service, and each prefix holds up to 10,000 numbers. That counts prefixes assigned to carriers, not numbers in use.
- Does a valid format mean a 423 number is in service?
- No. A format check only says the digits fit the North American Numbering Plan and that 423 is an assigned code. It cannot tell whether the number is connected, who answers it or which carrier serves it today, because numbers are reassigned and ported. A live carrier lookup reports the current carrier and line type, but even that is not proof someone answers.
- Can I check a list of 423 numbers for free?
- Yes. Paste them in the list tab above or upload a CSV to the bulk phone number validator: format, E.164, country and the numbering-plan line type are free for every row, with no account. Live carrier and line-type lookups come with Pro + Phone at $49.99/mo (5,000 a month).
Other area codes in Tennessee
All Tennessee area codes on the area code index.
Sources
Location, overlays, in-service date and dialling plan: NANPA NPA database, file dated 10/16/2026. Prefixes and rate centers: NANPA central office code assignments, 10/17/2026. Time zones mapped to the IANA time zone database. By the SimpleVerifier Team; how we build these pages.