Area code 303: Colorado
Area code 303 is a US state area code for Colorado, on Mountain Time. It has 784 prefixes in service across 13 rate centers, the largest being Denver, Longmont and Fort Lupton. It shares its area with 720 and 983, so local numbers there can start with any of them. Local calls there take 10 digits.
Local time in area code 303
America/Denver
Prefixes in service
784 of 792 possible
13 rate centers
Area code 303 facts
| Location | Colorado, United States |
|---|---|
| Time zone | Mountain Time |
| Overlays | 720, 983 |
| In service since | 1947, when the plan began |
| 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 |
Which cities and towns use area code 303?
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 303 rate centers with the most prefixes in service. 1 smaller ones aren't listed.
| Rate center | Prefixes |
|---|---|
| Denver | 735 |
| Longmont | 18 |
| Fort Lupton | 11 |
| Deckers | 5 |
| Keenesburg | 3 |
| Hudson | 2 |
| Georgetown | 2 |
| Deer Trail | 2 |
| Allenspark-Lyons | 2 |
| Strasburg | 1 |
| Bennett | 1 |
| Byers | 1 |
Source: NANPA central office code assignments, file dated 10/17/2026. Each prefix holds up to 10,000 numbers.
How do I dial a 303 number?
NANPA's dialling plan for 303: 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 303 | 303-555-0147 |
|---|---|
| From another US or Canadian area code | 1-303-555-0147 |
| From outside North America | +1 303 555 0147 |
| E.164, for CRMs and SMS tools | +13035550147 |
When did area code 303 start?
Area code 303 is one of the original codes NANPA lists from 1947. Today 303, 720 and 983 cover the same area as an overlay, which is why 10-digit dialling is needed for local calls there.
Tools for 303 numbers
- Area code lookup
Look up any code or a whole list of numbers, or find the codes for a state or city.
- 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 303 number tells you where it was issued, not what it is now.
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Area code 303 questions
- What state is area code 303?
- Area code 303 is in Colorado, United States. Its largest rate centers by number of prefixes are Denver, Longmont, Fort Lupton, Deckers and Keenesburg.
- What time zone is area code 303 in?
- Mountain Time.
- What area codes overlay 303?
- 720 and 983. 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 303 start?
- Area code 303 is one of the original codes NANPA lists from 1947.
- Is a 303 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 303 have?
- 784 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.
Other area codes in Colorado
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.