Area code 303 was implemented in 1947 as the original code for the whole state of Colorado, according to the Colorado Public Utilities Commission (PUC). Geographic splits in 1988 and 1995 took away other parts of the state. A 720 overlay arrived in 1998, and a 983 overlay was announced in 2022, so three area codes now serve the Denver region.
Quick answer
- 303 was implemented in 1947 and originally served all of Colorado. Today it shares the Denver metro region with 720 and 983.
- It was split twice: 719 in 1988 and 970 in 1995. 720 was added as an overlay in 1998.
- The state announced the 983 overlay on May 17, 2022. New service or added lines may receive 983 numbers starting June 17, 2022. Existing numbers do not change.
- Local calls within and between 303, 720, and 983 use 10 digits.
The essentials
303 area code: quick facts
| Area code | 303 |
| Coverage | The Denver metro area, shared with the 720 and 983 overlay codes |
| State | Colorado |
| Time zone | Mountain Time (MT) |
| Assigned | 1947 (FCC lists January 1947), the original code for all of Colorado |
| Splits from 303 | 719 (1988) and 970 (1995) |
| Overlay codes on the Denver region | 720 (1998) and 983 (announced May 17, 2022; may be assigned from June 17, 2022) |
| Dialing | 10 digits for local calls within and between the overlay codes |
| Country code | +1, the country code for the North American Numbering Plan |
How 303 became the Denver code
- 1947: The PUC says the 303 numbering plan area was the original one serving the entire state of Colorado, implemented in 1947. The FCC lists 303 as opening in January 1947.
- 1988: The 303 area undergoes a geographic split that creates area code 719, per the PUC. The FCC lists 719 as opening in March 1988.
- 1995: A second geographic split creates area code 970, per the PUC. The FCC lists 970 as opening in April 1995.
- 1998: Area code 720 is implemented as an overlay on 303, per the PUC. The FCC lists 720 as opening in June 1998.
- May 17, 2022: DORA announces that the PUC approved a 983 overlay for the existing 303/720 region.
- June 17, 2022: Customers requesting new service or an added line may be assigned a 983 number, per DORA. The FCC lists 983 as opening in June 2022.
Where area code 303 is used
DORA describes the 303, 720, and 983 region as the Denver metro area and nearby communities. Its 2022 announcement names Aurora, Boulder, Brighton, Castle Rock, Columbine, Englewood, Erie, Highlands Ranch, Lakewood, Littleton, Longmont, Thornton, Westminster, and Wheat Ridge.
That list describes the whole overlay region, not 303 alone. Because the codes overlap, a home or business in any of those places could have a 303, 720, or 983 number. The state pages we read give no county list, no street boundaries, and no list of communities for 303 on its own, and they do not say which other city names are inside the region. Confirm a specific address with your phone provider before you assume its area code.
Why relief was needed, and how the state decides
The PUC says area code relief is needed because new technologies, growing consumer demand for new devices, and population growth have increased demand for numbers. DORA said in 2022 that new numbers in the Denver area were in high demand.
The PUC describes the planning process this way. The numbering administrator (NANPA) notifies the state commission and the industry three years before it expects an area code to run out of prefixes. Industry and NANPA then work out options, which must follow FCC and state rules and the rate area boundaries, and the state commission makes the final decision. If a split is approved, the commission also decides which area keeps the existing code.
The PUC lists proceeding 20V-0192T, "Industry Petition for Overlay Relief (303/720)," on its telecommunications proceedings page. We did not find an official page that states the exhaust forecast that led to 983, or the date of the PUC decision, so this guide gives neither. The only official date we found is DORA's May 17, 2022 announcement.
Neighboring area codes in Colorado
The PUC describes how the other Colorado codes relate to 303. It does not describe where each applies, so the table gives relationships only. Use your provider or the NANPA area code map for territory.
| Code | Relation to 303 | Dates |
|---|---|---|
| 303 | Original code for all of Colorado | 1947 (FCC: January 1947) |
| 719 | Created when 303 underwent a geographic split | 1988 (FCC: March 1988) |
| 970 | Created by a second geographic split of 303 | 1995 (FCC: April 1995) |
| 720 | Overlay on 303 | 1998 (FCC: June 1998) |
| 983 | Overlay on the 303/720 region | Announced May 17, 2022; FCC: June 2022 |
| 748 | Not a 303 code. The PUC approved it as an overlay of 970 on November 20, 2023, to be assigned only once 970 is exhausted | Per the PUC FAQ, not yet assigned |
The 720 and 983 overlays and what they change
An overlay puts more than one area code on the same geography. The PUC says all current customers keep their area code and telephone number, and numbers from the new code may go to new customers or to those adding lines. Because two codes share a region, all local calls must be dialed with the area code plus the seven-digit number.
- Existing numbers: DORA says current numbers, including area codes, do not change.
- Local calls stay local: DORA says call pricing, coverage area, rates, and services do not change, and a local call stays local.
- Calls between the codes: local calls within and between the overlay codes use 10 digits.
- When 983 is assigned: DORA says that from June 17, 2022, customers requesting new service or an added line may get 983. The DORA announcement does not say whether providers must use up 303 and 720 numbers first.
| Code | Added | Where it applies |
|---|---|---|
| 303 | 1947 | Denver metro region, original code |
| 720 | 1998 | Overlay on 303 |
| 983 | May 17, 2022 announcement; assignable from June 17, 2022 | Overlay on the 303/720 region |
Time zone and daylight saving time
Denver is on Mountain Time. The tz database zone table lists Denver as America/Denver, labeled "Mountain (most areas)." The tz rules file shows that zone at UTC-7 with the U.S. daylight saving rules. The same table has a separate Idaho and Oregon zone, America/Boise, which is not in the Denver area.
Daylight saving time starts at 2:00 a.m. on the second Sunday of March and ends at 2:00 a.m. on the first Sunday of November, according to NIST. NIST credits the Energy Policy Act of 2005 for the current schedule. In 2026, NIST gives March 8 and November 1 as the change dates. Check the local time in Denver before you schedule a call from another zone.
How to dial a 303 number
North American numbers have three parts: a country code, a three-digit area code, and a seven-digit local number. NANPA says the ITU assigned country code 1 to the NANP area.
DORA says local calls within and between the 303, 720, and 983 area codes use 10 digits, and long-distance calls use 1 plus 10 digits. Three-digit numbers such as 911 still work, as do 211, 311, 411, 511, 611, 711, and 811 where already available.
DORA asks customers to make sure their equipment accepts 983 as a valid code. Its list includes contact lists, PBXs, fax machines, speed dialers, call forwarding, voicemail, medical alert devices, alarm systems, gates, and ankle monitors. It also says websites, stationery, checks, advertising, and ID tags should include the area code. The PUC adds, for business customers, message detail recording equipment, least-cost routing and toll restriction systems, and alarm circuits.
Caller ID and scams with a 303 number
The FTC says "Scammers can make any name or number show up on your caller ID" and calls this spoofing. Scammers can also match the first six digits of your own number, which the FTC calls neighbor spoofing.
- The FTC says a number like this on your caller ID could be faked.
- If you do pick up and do not recognize the caller, the FTC says to hang up.
- Letting an unknown call go to voicemail is one option, per the FTC.
- The FTC says call blocking is your best defense against unwanted calls.
A 303 number shows the code that was assigned, not who is calling or where they are. The sources we checked do not say that 303 numbers are targeted more than other codes. Because 720 and 983 share the same region, a 303, 720, or 983 caller ID is not a reliable sign that the caller is in Denver.
Business numbers in the Denver area
The 303 code identifies the Denver metro region, but it is not the only code there. Which code a new business line gets depends on the provider and the numbers it has available. DORA says only that 983 numbers may go to customers requesting new service or an added line, so ask your provider before you plan a campaign or print a number.
Because 303, 720, and 983 share one region and local calls between them use 10 digits, route calls by team or extension, not by area code. Publish the full 10-digit number everywhere, as DORA advises for websites, stationery, checks, and advertising.
Important: Whether a specific 303 number can be assigned to your business depends on your phone provider and its current inventory. This guide does not make claims about availability.
Before you use a 303 number
- Confirm the number is available from your provider, and get its terms in writing.
- Ask who owns the number and whether it can be moved to another provider if you switch.
- Ask whether a new line would be a 303, 720, or 983 number.
- Use 10-digit dialing on every system, including PBXs, fax machines, alarms, call forwarding, and voicemail.
- Print the full 10-digit number on stationery, cards, checks, and advertising.
- Route calls by team or extension, because three codes share one region.
- Check each site address. The state pages name communities, not street boundaries, so confirm the address with your provider.
- Plan for caller ID. A 303 number does not prove who is calling, and neighbor spoofing copies the first six digits of your own number.
Frequently asked questions
Which area is the 303 area code for?
Area code 303 serves the Denver metro area. The Colorado Department of Regulatory Agencies (DORA) says the 303, 720, and 983 area codes share one region that includes Aurora, Boulder, Brighton, Castle Rock, Columbine, Englewood, Erie, Highlands Ranch, Lakewood, Littleton, Longmont, Thornton, Westminster, and Wheat Ridge. The Colorado Public Utilities Commission (PUC) says 303 was implemented in 1947 as the original code for the entire state.
Is area code 303 being split or replaced?
No source we opened says so. The PUC says 303 was split in 1988 (creating 719) and 1995 (creating 970), and that 720 was added in 1998 as an overlay. DORA announced a 983 overlay in May 2022 and says current customers keep their numbers and area codes.
Do I need to dial 10 digits for a 303 number?
Yes. DORA says local calls within and between the 303, 720, and 983 area codes use 10 digits, and long-distance calls use 1 plus 10 digits. Three-digit numbers such as 911 still work, as do 211, 311, 411, 511, 611, 711, and 811 where already available.
Will a new line in Denver get a 983 number?
It may. DORA says that starting June 17, 2022, customers requesting new service or an added line may be assigned a 983 number. Which code you receive depends on your provider, so ask before you print or publish a number.
Does a 303 number mean the caller is in Denver?
Not always. The Federal Trade Commission (FTC) says scammers can make any name or number show up on caller ID, and neighbor spoofing copies the first six digits of your own number. A local-looking number is not proof of who is calling.
Sources · reviewed October 2026
Used for the May 17, 2022 announcement, the June 17, 2022 date from which 983 may be assigned, the list of cities, 10-digit local dialing and 1+10 long distance, the three-digit numbers that keep working, the statement that numbers and prices do not change, the equipment and stationery guidance, and the remark that new numbers are in high demand.
Colorado New Area Code 748 FAQ, Colorado PUC and Current Telecommunications Proceedings, Colorado PUC
Used for the 1947 original statewide code, the 1988 split (719), the 1995 split (970), the 1998 720 overlay, the 748 overlay of 970 approved November 20, 2023, the description of overlays, the reasons for relief, the planning process, the business equipment list, and proceeding 20V-0192T. puc.colorado.gov returns an error to automated requests, so the text was read from archived copies.
Numbering Resource Utilization in the United States, FCC, Table 6 and About NANPA, archived copy
Used for the opening dates of 303 (January 1947), 719 (March 1988), 970 (April 1995), 720 (June 1998), and 983 (June 2022). The archived NANPA page supports the country code 1 for the NANP area.
Phone Scams, FTC Consumer Advice and That is not your neighbor calling, FTC Consumer Alert
Used for the spoofing definition, the neighbor spoofing explanation, the advice to hang up on unknown callers, the voicemail option, and the call-blocking advice.
Daylight Saving Time, NIST, tz database zone table, and tz database North America rules
Used for the second-Sunday-of-March and first-Sunday-of-November rule, the Energy Policy Act of 2005, the 2026 change dates, the America/Denver zone entry labeled "Mountain (most areas)," and the zone using the U.S. daylight saving rules at UTC-7.