Area Code 303
Colorado
Area code 303 serves Colorado, primarily Denver, in the Mountain Time (MT) time zone. It has served the region since 01-Jan-1947.
Overlay Area Codes
This area code is part of an overlay region, meaning the same geographic area is served by multiple area codes. Overlay codes were introduced to meet growing demand for phone numbers without requiring existing customers to change their numbers.
This area code shares its geographic region with: area code 720 (Denver), area code 983 (Denver).
In service since: 01-Jan-1947
Area Code Splits
Parts of this area code’s original geographic region were later assigned new area codes through splits. When a split occurs, some customers in the original area code region are assigned the new area code.
Split into: area code 719 (Colorado Springs).
Historical Timeline of Area Code 303
Area code 303 was created on January 1, 1947 as one of the original 86 North American area codes, assigned to serve the entire state of Colorado. Denver was designated as a Regional Center under the original NANP hierarchy, with the code 303 indicating a single-code state. Over the next 75 years, the area code underwent two geographic splits and two overlays, reducing its territory from the full state to the Denver-Boulder metropolitan core and creating a three-code overlay complex with 720 and 983. Source: Wikipedia
- 1947: Created January 1 as one of the original 86 NANP area codes. Assigned to the entire state of Colorado. Denver designated as Regional Center. The middle digit 0 in the code 303 was reserved for states served by a single area code. Source: Wikipedia
- 1988: 719 split effective March 5, 1988 at 11:59 PM MST. Southeastern Colorado, including Colorado Springs, Pueblo, Leadville, and Alamosa, split off per NANPA Information Letter IL-87-03-045. Permissive dialing period ran through April 4, 1988. Source: NANPA IL-87-03-045
- 1995: 970 split effective April 2, 1995. Northeastern and western Colorado, including Fort Collins, Grand Junction, Vail, and Aspen, split off per NANPA Information Letter IL-94-09-012. Permissive dialing through October 1, 1995. Area code 303 was reduced to the Denver-Boulder area and became the only Colorado area code that does not border another state. Source: Wikipedia
- 1998: 720 overlay activated September 1, 1998 per NANPA Planning Letter PL-117. The Colorado PUC had initially proposed a wireless-only overlay, but a 1995 FCC ruling prohibited technology-specific area code overlays, forcing an all-services overlay. First overlay for the 303 NPA, requiring 10-digit dialing for all local calls. Source: NANPA PL-117
- 2022: 983 overlay activated June 17, 2022 per NANPA Planning Letter PL-563. Colorado PUC approved the overlay on May 21, 2021 under Decision No. C21-0310 in Proceeding 20V-0192T. NANPA had projected numbering exhaustion by Q2 2023. Network preparation began September 17, 2021. The test number assigned was 983-983-1983. The result was 23.8 million telephone numbers assigned to approximately 3.5 million people. Source: Colorado DORA
Colorado originally had a single area code (303) from 1947 until 1988. The state has since added 719 (1988), 970 (1995), 720 (1998), and 983 (2022), bringing the total to five area codes. The 303/720/983 overlay complex covers the Denver metropolitan area and north-central Colorado.
Unique Facts About Area Code 303
Area code 303 has several characteristics rooted in its history as one of the original 86 North American area codes from 1947. Source: Wikipedia
- Denver Regional Center designation: Denver was designated a Regional Center in the original 1947 NANP, and the code 303 was assigned with a middle digit of 0, the format reserved for states served by a single area code. This designation remained accurate for 41 years until the 719 split in 1988. Source: Wikipedia
- Only non-bordering Colorado code: After the 1995 split created area code 970 to cover the northern and western border regions, area code 303 became the only Colorado area code that does not border another state. It is entirely landlocked within Colorado's interior. Source: Wikipedia
- High per-capita number ratio: The 303/720/983 overlay complex has resulted in 23.8 million telephone numbers being assigned to an area with approximately 3.5 million people, roughly 6.8 numbers per person. Source: NANPA
- FCC wireless overlay ruling: Colorado's first overlay (720, 1998) was originally proposed as wireless-only by the Colorado PUC. The FCC's 1995 ruling prohibiting technology-specific area code overlays forced a change to an all-services overlay. This ruling affected overlay proposals nationwide. Source: Wikipedia
- 983 test number: The 983 overlay was assigned the test number 983-983-1983 during implementation. NANPA projected the 983 code would last approximately 25 years before requiring further relief. Source: Colorado DORA
Area code 303 served the entire state of Colorado alone from 1947 to 1988, making it the sole area code for the state for 41 years. The Denver metropolitan area continues to grow, driving the need for multiple overlay codes to meet numbering demand.
FCC Regulatory History
Area code 303 has been governed by six major regulatory actions spanning 35 years. These include two NANPA split orders, an FCC ruling prohibiting technology-specific overlays, two NANPA overlay planning letters, and a Colorado PUC decision approving the 983 overlay. Source: NANPA
| Year | Event | Docket | Regulatory Action & Impact |
|---|---|---|---|
| 1987 | 719 Split | IL-87-03-045 | NANPA split of 303 NPA creating 719 for southeastern Colorado. Split effective March 5, 1988. Permissive dialing through April 4, 1988. (NANPA) |
| 1994 | 970 Split | IL-94-09-012 | NANPA split of 303 NPA creating 970 for northeastern and western Colorado. Split effective April 2, 1995. Permissive dialing through October 1, 1995. (Wikipedia) |
| 1995 | FCC Overlay Ruling | FCC Order | FCC prohibited technology-specific area code overlays nationwide. Forced Colorado PUC to withdraw its wireless-only 720 overlay proposal and adopt an all-services overlay. (Wikipedia) |
| 1998 | 720 Overlay | PL-117 | NANPA approved all-services overlay of 720 on 303 NPA. 720 activated September 1, 1998. Required 10-digit dialing for all calls within the service area. (NANPA) |
| 2021 | 983 Approval | 20V-0192T | Colorado PUC approved 983 all-services distributed overlay for 303/720 NPA. Decision No. C21-0310 adopted modified Recommended Decision No. R21-0248. NANPA projected exhaustion by Q2 2023. (Colorado DORA) |
| 2022 | 983 Activation | PL-563 | NANPA implementation plan for 303/720/983 overlay. Network preparation began September 17, 2021. 983 activated June 17, 2022. Projected to last approximately 25 years. Test number: 983-983-1983. (Colorado DORA) |
Demographics & Economics
- Total Population
- 5,264,773
- Population Density
- 298 people/sq miabove U.S. average (U.S.: 94 people/sq mi)
- Median Household Income
- $97,215above U.S. median (U.S.: $78,538)
- Poverty Rate
- 8.6%below U.S. average (U.S.: 12.4%)
- Unemployment Rate
- 4.3%below U.S. average (U.S.: 5.2%)
- Education Attainment
- Bachelor's Degree+48.6%above U.S. average (U.S.: 35.0%)High School or Lower21.6%
Statistics are population-weighted aggregations from Census ACS 5-year estimates.See Sources for details.
Geographic Coverage
State
CO
Major Cities
- Denver
- Aurora
- Lakewood
- Thornton
- Arvada
- Westminster
- Centennial
- Boulder
- Highlands Ranch
- Longmont
- Loveland
- Castle Rock
- Broomfield
- Commerce City
- Parker
- Littleton
- Brighton
- Northglenn
- Dakota Ridge
- Englewood
- Ken Caryl
- Wheat Ridge
- Erie
- Lafayette
and 124 more cities
Time Zone
- Mountain Time (MT)
Current Time
County Coverage
Population-weighted county share based on aggregated ZCTA population (100% = total mapped population for area code 303).
| County | Population | Share |
|---|---|---|
| Denver, CO | 1,044,485 | 19.8% |
| Arapahoe, CO | 989,106 | 18.8% |
| Adams, CO | 854,477 | 16.2% |
| Jefferson, CO | 762,712 | 14.5% |
| Douglas, CO | 502,657 | 9.5% |
| Boulder, CO | 458,086 | 8.7% |
| Broomfield, CO | 214,846 | 4.1% |
| Weld, CO | 193,758 | 3.7% |
| Larimer, CO | 102,131 | 1.9% |
| Elbert, CO | 65,901 | 1.3% |
| Clear Creek, CO | 30,425 | 0.6% |
| Gilpin, CO | 29,241 | 0.6% |
| Park, CO | 12,498 | 0.2% |
| El Paso, CO | 4,450 | 0.1% |
Call Context
This area code covers a metropolitan region in CO with moderate to high population density, centered on Denver and surrounding communities.
Nearby Area Codes
Area codes geographically closest to 303.
Other Area Codes in Colorado
Area codes that also serve Colorado, linked for easy comparison.
Frequently Asked Questions
Common questions about area code 303 and how phone numbering works.
303 was the sole area code for the entire state of Colorado from 1947 until 1988 (41 years).
NANPA IL-87-03-045 — split created 719 for southeastern Colorado.
Phone numbers assigned to area code 303 are tied to where they were originally provisioned — not the caller's current location. This code serving roughly 5265k people covers Denver in CO, so a number originally set up there will retain the 303 prefix even if the owner moves or uses VoIP. Mobile phones keep their original number when users relocate, and businesses often adopt local area codes to establish a regional presence.
Start by looking up the area code on this site to understand its geographic context — area code 303 is associated with Denver in CO. For caller-specific details, use your carrier's caller ID features or check public directories. If you suspect fraud, you can report it to the FTC. To file a complaint about robocalls or spoofed numbers, visit the FCC Consumer Complaint Center. You can also register with the National Do Not Call Registry.
When an area's available number pool runs low, regulators introduce an "overlay" code covering the same territory. Both codes coexist, and new numbers are assigned from whichever has availability. Area code 303 serves the Denver region in CO, where growing demand for phone numbers necessitated an additional code. This area code shares its region with area code 720, area code 983. Learn more in our overlay vs split guide.