The 303 area code serves the Denver metropolitan area and Boulder, the population and economic heart of Colorado. One of the original area codes assigned in 1947, 303 covers the state capital and the fast-growing Front Range suburbs at the foot of the Rocky Mountains.
Quick Summary of the 303 Area Code
| Area Code | 303 |
| State | Colorado (CO) |
| Region | Denver Metropolitan Area & Boulder |
| Major Cities | Denver, Aurora, Lakewood, Boulder, Arvada, Westminster, Thornton, Centennial |
| Time Zone | Mountain Time (MT) – MST / MDT |
| Dialing Format | 10-digit dialing required |
Geographic Coverage
The 303 area code is centered on the city of Denver and blankets the surrounding metro, including Aurora and Centennial to the southeast, Lakewood and Arvada to the west, Westminster and Thornton to the north, and the university city of Boulder to the northwest. It shares its footprint with the 720 and 983 overlays, together covering the densest part of Colorado’s Front Range.
Time Zone
The 303 area code observes Mountain Time (MT). Clocks follow Mountain Standard Time (UTC−7) in winter and shift to Mountain Daylight Time (UTC−6) from mid-March through early November. All of Colorado is on Mountain Time. From the West Coast, this region is one hour ahead of Pacific Time, so a 9:00 AM call in California reaches a 303 number at 10:00 AM local time.
Tip: Business hours across the 303 region generally run 9:00 AM to 5:00 PM Mountain Time, Monday through Friday.
How to Dial a 303 Number
Because area code 303 operates as part of an overlay, 10-digit dialing is mandatory for every local and long-distance call. You must dial the full 10-digit number (303 + the seven-digit line number) even when calling a neighbor across the street. For international callers, dial your country’s exit code, then +1 (the North American country code), then 303, followed by the seven-digit local number.
Scam Alerts for the 303 Area Code
Like every U.S. area code, 303 has been used by scammers who spoof local numbers to appear trustworthy. Residents in Denver, Aurora, Lakewood, Boulder, Arvada, Westminster, Thornton, Centennial should stay alert to the following common tactics:
| Scam Type | What to Watch For |
|---|---|
| IRS / Tax Scams | Callers claiming you owe back taxes and threatening arrest unless you pay immediately. |
| Utility Shut-off | Fake Xcel Energy reps demanding payment to avoid disconnection. |
| Bank Fraud Alerts | Robocalls impersonating your bank about “suspicious activity” to phish account details. |
| Grandparent Scam | A caller posing as a relative in trouble asking for emergency wire transfers. |
If you receive a suspicious call from a 303 number, take these steps to protect yourself:
- Do not share personal information such as Social Security numbers, bank details, or passwords over the phone.
- Hang up and verify by calling the organization back using an official number from its website.
- Report the call to the FTC at reportfraud.ftc.gov and to the Colorado Attorney General’s Office.
- Block the number and consider registering with the National Do Not Call Registry.
Red Flag: Legitimate agencies such as the IRS, Social Security Administration, or your local utility company (Xcel Energy or Colorado Springs Utilities) will never demand immediate payment by gift card, wire transfer, or cryptocurrency. Any 303 caller making such a demand is a scammer.
History and Economy of the 303 Region
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Area code 303 is one of the original 86 codes established in 1947, and it once covered the entire state of Colorado before 719 (1988) and 970 (1995) were split off. As the Denver metro boomed, the 720 overlay was added in 1998 and a third overlay, 983, followed in 2023 across the same territory. The regional economy is broad and modern: Denver is a hub for aerospace, technology (part of the “Silicon Mountain” corridor), energy, telecommunications, and finance, while Boulder adds a concentration of federal research labs, the University of Colorado, and a thriving startup scene. Denver International Airport, one of the busiest in the world, anchors a major logistics and travel economy.
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Looking Up a 303 Number
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To identify a 303 caller, use a reverse phone lookup service or search the full 10-digit number online. Many Denver-area businesses, government offices, and healthcare providers list their 303 numbers publicly, so a quick search often confirms a legitimate caller. For unknown numbers, let the call go to voicemail – genuine callers usually leave a message.
Nearby & Related Area Codes
Colorado is served by several area codes. If you are researching 303, these neighboring and overlay codes are worth knowing:
- 720 – Denver metro overlay (same region)
- 983 – Denver metro overlay (same region)
- 719 – Southern CO / Colorado Springs
- 970 – Northern & Western CO / Fort Collins
You can also browse our full directory of Colorado area codes for more regional guides.
↑ See the complete list of All US Area Codes by State – every area code across all 50 states in one directory.
Explore Neighboring States
Researching area codes just across the state line? Start with these codes in the states that border Colorado:
- Wyoming – area code 307
- Nebraska – area code 402
- Kansas – area code 316
- Oklahoma – area code 405
- New Mexico – area code 505
- Utah – area code 801
- Arizona – area code 602
Frequently Asked Questions
Where is the 303 area code located?
The 303 area code covers the Denver metropolitan area and Boulder, including Aurora, Lakewood, Arvada, Westminster, Thornton, and Centennial.
Do I need to dial 10 digits for 303?
Yes. Because 303 shares overlays with the 720 and 983 area codes, you must dial all 10 digits for every local call.
What time zone is the 303 area code in?
The 303 area code is in the Mountain Time Zone (MST/MDT), like all of Colorado.
What other area codes overlay 303?
The 720 (added 1998) and 983 (added 2023) area codes are overlays covering the same Denver-area region as 303.
Related 303 Guides
- Is a 303 call safe? Read Is area code 303 a scam? Spam & safety guide.
- Local coverage: see the Denver area code guide.
- Worried about spam or robocalls? Browse our Scam Alerts directory.