Colorado · Mountain Time
720 Area Code
Area code 720 is in Colorado, serving Denver, Boulder and the surrounding Front Range metro area in north-central Colorado. It is in the Mountain Time zone. It shares its territory with overlay codes 303 and 983, so 10-digit dialing is required.
Last updated October 1, 2026 · Source: NANPA
Where is the 720 area code?
720 is a Colorado area code covering Denver, Boulder and the surrounding Front Range metro area in north-central Colorado. In the wider directory it sits in the West region.
Cities in the 720 area code
- Denver
- Aurora
- Lakewood
- Thornton
- Arvada
- Westminster
- Centennial
- Boulder
- Highlands Ranch
- Littleton
- Broomfield
- Longmont
- Castle Rock
- Parker
- Commerce City
- Brighton
Counties served by 720
Denver County, Arapahoe County, Jefferson County, Adams County, Douglas County, Boulder County and Broomfield County.
720 overlay codes and dialing
The 720 territory is covered by an overlay of 3 area codes: 303, 720, 983. All of them serve the same geographic area, and the original code is 303. Because more than one code covers the same ground, 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.
History of the 720 area code
720 went into service on June 1, 1998 as an overlay of 303, relieving number exhaustion in the Denver area. Rather than splitting the region, the overlay lets existing customers keep their numbers while new lines draw from the added code. Learn more in our overlay guide.
Is 720 a scam or spam risk?
720 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 720 number on your screen is no guarantee the caller is in Denver, CO 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 7XX 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
720 area code FAQ
Where is the 720 area code?
The 720 area code is in Colorado, covering Denver, Boulder and the surrounding Front Range metro area in north-central Colorado, in the West region.
What cities are in the 720 area code?
Cities in the 720 area code include Denver, Aurora, Lakewood, Thornton, Arvada, Westminster, Centennial, Boulder, Highlands Ranch and Littleton.
What time zone is 720 in?
720 is in the Mountain Time zone.
What is the overlay for the 720 area code?
720 shares its territory with 303 and 983. All 3 codes (303, 720, 983) serve the same area, so 10-digit dialing is required for every call.
When did the 720 area code start?
720 went into service on June 1, 1998 as an overlay of 303.
Do I have to dial 10 digits for 720?
Yes. Because 720 is an overlay area, you must dial the full 10-digit number (area code + 7 digits) for every call.
Is 720 a toll-free or premium code?
No. 720 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.