Colorado · Mountain Time
303 Area Code
The 303 area code is a telephone area code in Colorado, covering Denver and the surrounding area. It lies in the Mountain Time zone.
Last updated June 5, 2026
Where is the 303 area code?
303 serves Denver and nearby communities in Colorado. In the wider directory it sits in the West region.
Overlay codes serving Denver
Denver is served by an overlay of 3 area codes: 303, 720, 983. Because more than one code covers the same area, 10-digit dialing is mandatory — you must dial the area code for every local call. New phone lines may be assigned any of these codes, so Denver numbers are no longer tied to a single prefix.
History of the 303 area code
303 is one of the original area codes assigned in 1947, when AT&T and Bell Laboratories created the North American Numbering Plan and divided the country into the first 86 numbering plan areas. It has served the Denver area ever since.
Is 303 a scam or spam risk?
303 is a legitimate geographic area code, not a premium or toll line, so a call from it costs you nothing extra. That said, scammers frequently spoof real local area codes to look familiar on caller ID. A genuine 303 number on your screen is no guarantee the caller is local or trustworthy. See spam & scam-risk area codes for how spoofing works and how to respond.
Other Colorado area codes
Explore more
See every code in Colorado, compare codes across the West region, or view all Mountain Time codes. You can also browse the 3XX block or the complete numeric list of US area codes.
New to how this all works? Start with how area codes work, then read up on overlays, 10-digit dialing, and spam & scam-risk codes. To check another number, use the area code lookup tool.
Quick answers
303 area code FAQ
Where is the 303 area code?
The 303 area code is in Colorado, serving Denver and the surrounding area in the West region.
What time zone is 303 in?
303 is in the Mountain Time zone.
Do I have to dial 10 digits for 303?
Yes. Because Denver is an overlay area, you must dial the full 10-digit number (area code + 7 digits) for every call.
Is 303 a toll-free or premium code?
No. 303 is a standard geographic area code, so calling it costs the same as any local or long-distance call on your plan. Toll-free calls use 800, 888, 877, 866, 855, 844 or 833.