Where is area code 303?
NANPA assigns 303 to Colorado. The source report does not provide city-level coverage for this record, so this page does not guess a particular city. Browse other codes in Colorado
Verified area-code information
303 Area Code
303 is an in-service United States area code assigned to Colorado. It identifies a numbering region, not a caller’s current location.
Official Numbering RegionVerified NANPA Assignment
ColoradoArea Code 303
Country: United States•Time Zone: Mountain•Overlays: 720, 983•In Service: 01-Jan-1947
- Numbering country
- United States
- Area-code type
- Geographic
- Numbering region
- Colorado
- Time-zone information
- Mountain
- In service since
- 01-Jan-1947
View the official area-code maps ↗. Maps show numbering areas, not a caller’s location.
Time zones associated with 303
NANPA lists Mountain for this numbering area. These are numbering-region time zones, not a caller’s current location.
Mountain time
An area code can span more than one time zone. Local daylight-saving rules may differ.
What area codes overlay 303?
The NANPA source lists 720, 983 in the same overlay complex. An overlay can serve the same broad numbering area; individual numbers still do not prove where a person is.
How do you dial a 303 number?
Use the North American country calling code +1 followed by the three-digit area code and seven-digit local number. For example, write the pattern as +1 303 XXX XXXX. Local dialing rules and charges depend on your location and provider. Check a supported dialing format or check NANPA’s 10-digit dialing list.
Assigned prefixes in 303
NANPA’s US report listed 784 assigned prefixes on 2026-09-29. These are code assignments, not a count of active phone numbers or proof of a caller’s current carrier. Search any US area code and prefix.
Top rate-center labels by assigned prefixes
| Rate center | Assigned prefixes |
|---|---|
| DENVER | 735 |
| LONGMONT | 18 |
| FORTLUPTON | 11 |
| DECKERS | 5 |
| KEENESBURG | 3 |
Top listed companies by assigned prefixes
| Assignment company | Assigned prefixes |
|---|---|
| QWEST CORPORATION | 448 |
| CELLCO PARTNERSHIP DBA VERIZON WIRELESS - CO | 60 |
| LEVEL 3 COMMUNICATIONS, LLC - CO | 58 |
| T-MOBILE USA, INC. | 39 |
| NEW CINGULAR WIRELESS PCS, LLC | 35 |
303 prefix lookup
784 assigned prefixes are listed for this area code. Search NANPA’s US central-office code assignments. The listed company and rate center describe an assignment; number portability means they cannot identify the current carrier, subscriber, or caller.
The area-code file loads when you search. The three-digit prefix stays in your browser.
Check a number with area code 303
Enter the full ten-digit number to see its structure and formatting. The check stays in your browser.
Check a 303 number
Enter a 10-digit +1 North American number. We check its structure and area-code record, not the caller’s identity or whether the line is active.
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Received an unfamiliar call?
The displayed number may be spoofed. Do not rely on an area code as proof of caller identity. If the caller claims to represent a business, end the call and contact that business using a number you found independently.
Common questions about 303
What time zone is area code 303 in?
303 is assigned to Colorado, and the NANPA record associates it with Mountain time. A phone number does not reveal its owner’s current time zone. The clock above uses a representative time zone for the numbering area.
Does 303 mean the caller is in Colorado?
No. An area code is an assignment, and a person can travel, move, use internet calling, or display a spoofed number.
Can this page identify who called?
No. OfficialAreaCode has no live subscriber directory or spam-report database.