303 Area Code
Denver, Colorado
Area code 303 is located in Denver, Colorado. It covers Denver, Boulder, and surrounding areas in the Mountain time zone (UTC-7). Administered by NANPA.
Where is area code 303?
Area code 303 is located in Denver, Colorado. It covers Denver, Boulder, and surrounding areas in the Mountain time zone (UTC-7).
Area code 303 is overlaid by area code 720. Both codes serve the same geographic region and require 10-digit dialing for local calls.
Cities Covered by Area Code 303
Area code 303 primarily serves the Denver area of Colorado. The exact coverage includes Denver, Boulder, and Aurora (part), along with surrounding communities and suburbs.
Time Zone
Mountain Time — UTC-7
Area code 303 operates in the Mountain Time Zone. When calling 303 numbers from a different time zone, be sure to account for the time difference to reach people during business hours.
About Area Code 303
Area code 303 was introduced in 1947 as a geographic area code serving Denver, Colorado. As demand for phone numbers grew, overlay code 720 was added to the same region, requiring 10-digit dialing for local calls. Area codes are administered by NANPA (North American Numbering Plan Administration), the organization responsible for managing phone number resources in the US and Canada.