One of the original 1947 North American area codes and Colorado's sole area code for 40 years, 303 now serves the Denver-Boulder metropolitan area within a three-code overlay complex (303/720/983).
The essentialsNumbering data · NumberResearch · as of 2026-09-18
Place
Denver
Type
geographic
Status
in service
In service since
1947
Projected exhaust
2069 Q2
Status, dates and counts are read from NumberResearch (NANPA / CNAC / FCC records). Assignment records show initial assignees, not the carrier serving a number today.
A · Where it is
Where 303 is
North-central Colorado: Denver, Boulder and surrounding Front Range suburbs..
Communities served wholly or partly by 303:
DenverBoulderAuroraLakewoodLittletonLongmontBroomfieldCastle Rock
Originally covered the entire state; progressively reduced by the 719 and 970 splits.
B · Relationships
How it relates to other codes
The codes 303 was split from, spawned, or shares its area with. A split divides the map and changes some numbers; an overlay shares the same ground and changes none — what's the difference?
Spawned · 1988719Colorado SpringsSoutheastern Colorado (Colorado Springs, Pueblo) split off from 303.
Spawned · 1995970Fort CollinsNorthern and western Colorado split off from 303.
Overlay · 1998720Denver (overlay)All-services overlay of the 303 Denver-Boulder area.
Overlay · 2022983Denver (overlay)Third overlay added to the 303/720 complex.
What's changing. Overlaid — part of the 303/720/983 Denver-metro overlay complex; ten-digit dialing mandatory.
C · History
How 303 got here
1947
Established as one of the original NANP area codes, covering the entire state of Colorado.
Source: Wikipedia
1988-03-05
Area code 719 split off, removing southeastern Colorado.
Source: Wikipedia
1995-04-02
Area code 970 split off, removing northern and western Colorado; 303 retained the Denver metro.
Source: Wikipedia
1998-09-01
Area code 720 added as an overlay; ten-digit dialing required.
Source: Wikipedia
2022-06-17
Area code 983 activated as a third overlay after projected exhaustion by 2023.
Source: Wikipedia
D · Capacity
How full it is
Prefixes assigned
800
Prefixes available
0
Thousands-blocks assigned
1,014
Prefix-assignment counts describe allocation to carriers, not how many individual numbers are in use. Full technical records: NumberResearch ↗.
Live status, dates, assignment counts and exhaust forecast — data as of 2026-09-18 (CC BY 4.0).
Place, relationships and history above are compiled by North American Numbers from the sources listed and last checked 2026-09-18. A check date is not an expert review — see how this is made. Flag an error.
North American Numbers