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US area code · Colorado

303 area code

Where the 303 area code is, its overlay and how to dial a +1 303 number from anywhere.

CoversDenver, ColoradoTime zoneMountain (MT)TypeOverlay
Quick answer

The 303 area code is in Denver, Colorado, United States (Mountain (MT)). To call from abroad: +1 303 555-0123. It is an overlay, so all 10 digits are dialled.

StateColorado
Main areaDenver
Time zoneMountain (MT)
TypeOverlay
10-digit dialingRequired
In service since01-Jan-1947

The 303 area code is a geographic North American Numbering Plan (NANP) code covering Denver, Colorado. It has been in service since 01-Jan-1947 and sits in the Mountain (MT) time zone.

Overlay 303 shares its region

Several area codes cover the same geographic area, so two neighbours can have different codes. Because of the overlay, you must dial all 10 digits (area code + number) even for local calls.

303720983

How to dial a 303 number

From abroad+1 303 555-0123
Within the US / Canada1 303 555-0123
Locally (same area)303 555-0123

Cities in the 303 area code

A 303 number is usually in one of these places in Colorado — 12 counties.

Arvada JeffersonAurora Adams;ArapahoeBoulder BoulderBrighton Adams;WeldBroomfield Broomfield;JeffersonCastle Rock DouglasCastlewoodColumbineCommerce City AdamsDenver Adams;Arapahoe;Denver;JeffersonEnglewood ArapahoeHighlands RanchKen CarylLafayette BoulderLakewoodLittleton Arapahoe;Douglas;JeffersonLongmont Boulder;WeldLoveland LarimerNorthglennParker DouglasSouthglennThorntonWestminster AdamsWheat Ridge Jefferson

Other Colorado area codes

719720748970983

Frequently asked questions

Where is the 303 area code?

The 303 area code is in Denver, Colorado, United States (Mountain (MT)).

Is 303 an overlay area code?

Yes. 303 overlays the same region as 720, 983, so callers dial all 10 digits.

Do I have to dial 10 digits for 303?

Yes — dial the area code plus the seven-digit number.

How do I call a 303 number from another country?

Dial your exit code (or +), then 1, then 303, then the number: +1 303 555-0123.

Source: NANPA numbering plan. An area code covers a region, not a precise address — a 303 number does not pinpoint a street or ZIP code.

Number holders in area code 303

Each prefix (the three digits after the area code) is assigned by NANPA to one telephone company. 800 prefixes are in use in 303, shared by 29 companies. The largest holders:

CompanyPrefixesShare
Qwest Corporation44956%
Cellco Partnership Dba Verizon Wireless608%
Level 3 Communications, LLC587%
T-Mobile USA, Inc.395%
New Cingular Wireless PCS, LLC354%
Spok, Inc.314%

Source: NANPA central office code assignments. A number keeps its original prefix when it is ported to another carrier.

Complaints about 303 numbers

Reports to the FTC, last 30 days
901
Recorded messages or robocalls
54%
Rank among area codes
#55 of 670
Most reported subjects
Other (514)
Dropped call or no message (103)
Medical & prescriptions (82)

Period Aug 26 – Sep 24, 2026. These are the numbers shown on the caller ID of the reported calls; many are spoofed and do not belong to the real caller.

Source: US Federal Trade Commission, Do Not Call reported calls data (daily files).

All US area codes United States +1 Map of area code 303 — cities & rate centres

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