303 area code — Denver, CO geographic

Data: NANPA public reports, current as of July 28, 2026.

The 303 area code covers Denver, Colorado, Mountain time zone, and dates back to January 1, 1947. It is part of the 303/720/983 overlay complex — these codes share the same territory. Note that porting and VoIP mean a 303 number can be used from anywhere — the code marks where the number was assigned.

784 central-office prefixes are currently active in this code, spread across 27 code-holding carriers. Thousands-block pooling applies to 228 prefixes, so a single prefix can belong to several carriers. Its prefixes map to 13 distinct rate centers.

NANPA projects numbering capacity for the 303/720/983 complex to exhaust in 2Q 2069.

Dialing: 10D locally, 10D to other codes (1+10 permissible at each service providers discretion).

Among Colorado codes, 303 stands out as the oldest area code in Colorado, in service since 1947.

To check where a specific 303 number was issued, look up its six-digit prefix; to check who is actually calling, ignore the display and verify through an official callback number — caller ID is assertable and routinely spoofed.

It has since spawned 719 (1988), 970 (1995), 720 (1998), 983 (2022).

Largest localities in 303

FAQ

Is 303 a toll-free number?

No. 303 is a geographic code; calls are billed like any other domestic call. Toll-free codes are 800, 833, 844, 855, 866, 877 and 888.

Why do 720 and 303 cover the same place?

They are overlays: when a code runs low on numbers, a new code is added over the same territory instead of splitting it. The 303/720/983 complex shares one service area, and local calls are dialed with 10 digits.

Will 303 run out of numbers?

NANPA's current forecast projects exhaust in 2Q 2069 — decades of capacity remain.