Direct answer
Area code 720 serves the Denver-Boulder metro area along the Front Range in Colorado. It is in the Mountain Time, and ten-digit dialing is required there.
Facts
| Area code | 720 |
| State | Colorado (CO) |
| Region | the Denver-Boulder metro area along the Front Range |
| Time zone | Mountain Time |
| Overlays | 303/720/983 |
| In service since | 1 June 1998 (parent 303) |
| Dialing rule | Yes — ten-digit dialing is required in this overlay area. |
Areas covered
The 720 footprint covers Denver, Aurora, Boulder, Lakewood, Thornton, Westminster, Arvada, Wheat Ridge, Golden, Englewood, Longmont, Broomfield, Littleton, and Castle Rock. That list describes the area the code serves today, not the larger territory it may have covered when it was first assigned. Colorado observes daylight saving time: Mountain Standard Time in winter and Mountain Daylight Time in summer. This is different from Arizona, where 602 stays on Mountain Standard Time year-round. Callers in this area should always dial the full ten-digit number, including the area code, even for a local call.
History
Area code 303 was Colorado’s original 1947 code for the entire state. Area code 719 split off in 1988 for Colorado Springs and the south, and 970 split off in April 1995 for the north-east and west, reducing 303 to the Denver-Boulder area. Area code 720 was added as Colorado’s first overlay, and NANPA records 720 in service on 1 June 1998, settling an earlier claim of 1 September 1998. Area code 983 was added as a second overlay, and NANPA Planning Letter PL-563 records 983 in service on 17 June 2022, which the NANPA search tool also confirms. Denver-Boulder numbers can therefore carry 303, 720, or 983.
Dialing
Dialing rule: Yes — ten-digit dialing is required in this overlay area. The reason is the overlay structure in the facts table above, except where this page states a different reason, as it does for 616. From outside the United States, the country code for the United States is 1, followed by the area code and the local number. This page explains the area code only; it does not identify who owns a number or where a phone is.
Calls and spoofing
A call that shows a familiar area code is not proof of who is calling. Caller ID can be spoofed, so a number that looks local may come from anywhere. Do not share personal or financial details because of the number on the screen, and hang up and call back on a number you trust if a caller asks for money, codes, or account access. This site does not identify callers or phone owners, and it does not list reported spam numbers.
Related codes
303, 983 (overlay complex).
Frequently asked questions
Where is 720 area code?
Area code 720 is in Colorado, covering the Denver-Boulder metro area along the Front Range. It does not cover the whole state.
What time zone is 720 area code?
Area code 720 is in the Mountain Time. Colorado observes daylight saving time: Mountain Standard Time in winter and Mountain Daylight Time in summer. This is different from Arizona, where 602 stays on Mountain Standard Time year-round.
What area codes overlay 720?
The overlay codes for 720 are 303; 983. The full overlay group is 303/720/983. New numbers in the same territory can carry any code in the group.
Do I need to dial 10 digits for 720?
Yes — ten-digit dialing is required in this overlay area.
When did 720 area code go into service?
Area code 720 has been in service since 1 June 1998 (parent 303).
Sources
NANPA area code search; NANPA Planning Letter PL-563; Area codes 303, 720, and 983
Based on a recent search of NANPA and official sources.
This website provides general information about North American area codes, compiled from public sources including NANPA. It is not affiliated with or endorsed by the FCC, NANPA or any telephone carrier. Area code details can change; confirm with your carrier or the official NANPA website. This site does not identify callers or phone owners.