Quick answer
The 303 area code serves Denver, Colorado in the Mountain Time (MT) (UTC-7 / UTC-6 DST). Assigned in 1947, it covers Denver-Boulder Metro including Denver, Boulder, Lakewood. Overlay codes: 720, 983.
- Region
- Denver-Boulder Metro, CO
- Time zone
- MT (UTC-7)
- Assigned
- 1947
- Population
- ~3,500,000
- Local time now
- · live
Where is area code 303?
The 303 area code is a North American Numbering Plan geographic code serving Denver and the surrounding Denver-Boulder Metro region in Colorado. Assigned by the North American Numbering Plan Administration in 1947, it currently serves approximately 3,500,000 residents on the Mountain Time (MT) (UTC-7 / UTC-6 DST). It shares geography with overlay codes 720, 983.
Cities served by the 303 area code
The 303 area code covers 6 major cities and towns across the Denver-Boulder Metro region:
| City | State |
|---|---|
| Denver | CO |
| Boulder | CO |
| Lakewood | CO |
| Littleton | CO |
| Aurora | CO |
| Broomfield | CO |
Businesses across Denver and surrounding cities use 303 numbers to project local presence and lift call answer rates. Industry studies of local presence dialing consistently report answer-rate gains of 20–40% over toll-free or out-of-area numbers — a caller ID that matches the recipient's region looks familiar and gets picked up.
303 area code time zone and business hours
The 303 area code is in the Mountain Time (MT) zone (UTC-7 / UTC-6 DST). Standard business hours in 303 run 9 AM to 5 PM MT.
If you're calling into 303 from a different time zone, factor in the offset. For example, an Eastern Time business calling 303 at 9 AM ET reaches Denver at 7 AM MT — likely outside standard business hours.
History of the 303 area code
The 303 area code was one of the original 86 area codes assigned in 1947 when the North American Numbering Plan was first deployed. As Denver grew and number demand increased, overlay codes 720, 983 were added to serve the same geographic region — a common solution that avoids forcing existing subscribers to change their numbers.
Is the 303 area code safe? Spam and scam calls
303 is a legitimate geographic area code for Denver — it is not a scam code or a premium-rate prefix, and a call from a 303 number is most likely a genuine local caller. The risk is not the area code itself but a tactic called neighbor spoofing: scammers fake their caller ID so an unwanted call appears to come from your own area code, because people answer familiar numbers more readily.
If you get an unexpected 303 call, a few signals point to a likely scam — a pre-recorded message, urgent pressure to act now, a demand for payment by gift card or wire transfer, or anyone asking for passwords, Social Security, or account numbers. Let suspicious calls go to voicemail, never share personal information, and report fraud to the FTC at reportfraud.ftc.gov. The FCC consumer guide on spoofing explains your rights under the Truth in Caller ID Act. A real Denver business will leave a clear voicemail and will not pressure you.
US carriers verify caller ID with the STIR/SHAKEN framework, which flags many spoofed numbers as "Spam Likely" before they ring. DialPhone 303 numbers are registered for STIR/SHAKEN attestation, so calls from your business are verified as genuine and reach customers without a false spam label. See the DialPhone guide to VoIP security for more.
Why get a 303 area code number for your business?
Getting a 303 number gives your business three measurable advantages over a toll-free or out-of-area number:
- Local trust signal. Customers in Denver recognize 303 as their home area code. Caller ID matching builds immediate credibility for service businesses, sales outreach, and patient communication.
- Higher answer rate. Calls from a familiar local area code are answered far more often than unknown or toll-free numbers — industry measurements of local presence dialing put the lift at 20–40%, which matters most for outbound sales, appointment confirmations, and time-sensitive service callbacks.
- Targeted marketing. Businesses serving Denver and the broader Denver-Boulder Metro can advertise a local number across print, radio, billboards, and digital channels for higher conversion than a national 800 number.
For businesses in Denver and surrounding cities, top industries that benefit from local 303 presence include Professional Services, Healthcare, and Retail. DialPhone's AI receptionist is available for every 303 number — never miss a call, even after standard business hours.
How to get a 303 area code number
Setting up a 303 business number with DialPhone takes under 10 minutes:
- Sign up for a DialPhone plan. Choose any plan starting at $24/user/month. Free 14-day trial, no credit card required.
- Search available 303 numbers. Filter the DialPhone number inventory by area code, city, or pattern.
- Choose your number and configure. Assign your new 303 number to a user or team, set up call routing, voicemail, AI receptionist, and business SMS.
- Port your existing number (optional). Already have a 303 number? Free number porting in 2 to 5 business days with zero service interruption.
New to local numbers? The complete guide to getting a local phone number covers choosing the right area code, porting an existing line, and avoiding spam flags.
303 area code overlay codes
The Denver-Boulder Metro region is served by multiple overlay area codes:
| Area Code | Coverage |
|---|---|
| 303 | Primary area code for Denver-Boulder Metro, assigned 1947 |
| 720 | Overlay — same geography (assigned 1998) |
| 983 | Overlay — same geography (assigned 2022) |
All overlay codes serve the same Denver region. New subscribers may be assigned any available code; existing numbers retain their original prefix.
AI receptionist for 303 area code businesses
Every DialPhone 303 number includes optional AI receptionist coverage, available 24/7. The AI handles calls when your team is unavailable — answering common questions, booking appointments, routing urgent callers to on-call staff, and capturing voicemail with full transcription and intent tagging.
For businesses in Denver that handle high call volume, run extended hours, or need bilingual support (especially valuable in service areas with diverse customer bases), the AI receptionist reduces voicemail backlog and improves first-call resolution.
All area codes in Colorado
Colorado has 5 active geographic area codes. The 303 area code is part of the same numbering plan as the codes listed below — calls between them are typically local within the state, depending on the carrier.
Nearby area codes
Related area codes in Colorado and the Mountain Time (MT) region:
- 719 area code — Colorado Springs, Colorado
- 720 area code — Denver, Colorado
- 970 area code — Fort Collins, Colorado
- 983 area code — Denver, Colorado
- 208 area code — Boise, Idaho
- 307 area code — Cheyenne, Wyoming
All Colorado area codes → · Browse all US area codes →
More area codes: ← 302 Wilmington · 304 Charleston →
How We Tested
DialPhone re-verifies every area code page every 90 days. Area code geography, timezone, and overlay data come from the official North American Numbering Plan Administration (NANPA) database. Pricing reflects the published DialPhone plan tiers — see the pricing page for current details. Number availability varies; check the DialPhone signup flow for live inventory in the 303 region.
What We Don't Like
- Number availability is finite. Popular Denver area codes can be inventory-constrained — request specific vanity patterns early.
- Porting timing varies. Most 303 ports complete in 2-5 business days; complex multi-line legacy contracts can take 7-10.
- HIPAA tier required for healthcare. The Core $24 plan doesn't include a BAA — healthcare users need Advanced ($34) or above.