303 Area Code: Denver, Colorado
Area code 303 serves Denver and Longmont, Colorado in the Mountain time zone, in service since 1947. Consumers have filed 9,567 unwanted-call complaints against 7,397 different 303 numbers, 745 of them with the FTC in the last 30 days. Look up the exact number that called you below.
Area code 303 at a glance
- State
- Colorado
- Main cities
- Denver, Longmont + 7 more
- Counties
- Denver County, Boulder County, Weld County, Douglas County + 3 more
- Local time
- —Mountain
- In service since
- 1947
- Local dialing
- 10 digits (area code + number)
- Exchanges
- 13 rate centers, 784 prefixes
Sources: NANPA area code and central office code records (refreshed weekly); cities and counties matched from US Census Bureau and USGS place names.
Most-reported 303 numbers
Ranked by FTC Do Not Call complaints this month, then all-time FTC and FCC complaints. Only numbers with enough complaints for a full report page are listed. Click one for what it was reported for and where.
What calls from 303 numbers are about
2,553 FTC Do Not Call complaints about 303 numbers since Jul 24. The most common named subject is medical & prescriptions, at 12% of complaints (79% of those were recorded messages). Overall, 69% of callers who answered said the call was a robocall.
FTC complaint subjects
- Other / unspecified1,38254%
- Medical & prescriptions29512%
- Dropped call / no message25110%
- Impostor (government, business, family)1687%
- Home improvement & cleaning1134%
- No subject given954%
- Warranties & protection plans924%
FCC complaints by call type, last 2 years
- Prerecorded Voice1,93777%
- Live Voice55622%
- Text Message161%
Live-voice calls are from a person; prerecorded calls are robocalls.
When 303 spam calls come in
35% of complaints that give a call time describe calls between 9am and 12pm. 96% came Monday to Friday, most on Tuesdays, the pattern of call-center robocall campaigns that run on business hours. Times are as consumers reported them to the FTC.
By hour of the day
By day of the week
Is it getting worse?
734 FTC complaints about 303 numbers in the last four weeks, down 11% on the four weeks before. FCC complaints about 303 numbers peaked in 2026 (2,278); the FTC's daily Do Not Call data has carried most of the volume since mid-2026.
FTC complaints per week
FCC complaints per year
Years shown as '15 to '26; the current year is partial.
Who gets these calls
82% of the FTC complaints about 303 numbers came from people whose own phone number also starts with 303, and 87% from Colorado. Calls that look local to the person receiving them are the signature of neighbor spoofing: robocallers display a number from your own area code because you're more likely to answer.
Where complainants live
- Colorado2,21287%
- Florida532%
- California241%
- Ohio201%
- Texas191%
What people with 303 numbers report
People whose own number starts with 303 filed 5,160 FTC complaints since Jul 24. 40% were about calls showing another 303 number. The most common named subject was debt-relief pitches.
Area codes on the calls they reported
- 303 (same code)2,08540%
- 72050410%
- 833 (toll-free)1844%
- 877 (toll-free)1663%
- 888 (toll-free)1453%
Busiest 303 prefixes this month
FTC complaints in the last 30 days, grouped by the first six digits. When one prefix collects complaints about many different numbers, a campaign is usually cycling through that block. The carrier is who NANPA assigned the prefix to, not who made the calls.
| Prefix | Complaints | Numbers | Carrier | Exchange |
|---|---|---|---|---|
| (303) 258-xxxx | 14 | 14 | Qwest (CenturyLink / Lumen) | Denver |
| (303) 316-xxxx | 10 | 10 | Qwest (CenturyLink / Lumen) | Denver |
| (303) 252-xxxx | 8 | 7 | Qwest (CenturyLink / Lumen) | Denver |
| (303) 232-xxxx | 8 | 7 | Qwest (CenturyLink / Lumen) | Denver |
| (303) 219-xxxx | 7 | 7 | MCImetro (Verizon Business) | Denver |
Carriers operating in 303
NANPA has assigned 784 303 prefixes (NPA-NXX central-office codes) across 13 rate centers: 23% to wireless carriers, 77% to landline and VoIP operators; 29% are pooled blocks shared by several carriers. The newest assignment was 2025-01-16. The carrier holding a prefix is who the number was issued through. It says nothing about who is calling, since caller ID is routinely spoofed.
| Carrier | Type | Prefixes | Rate centers | Newest assignment |
|---|---|---|---|---|
| Qwest (CenturyLink / Lumen) | Incumbent landline (ILEC) | 448(57%) | 8 | — |
| Verizon Wireless (Cellco Partnership) | Wireless | 60(8%) | 3 | 2025-01-16 |
| Level 3 (Lumen) | Competitive / VoIP (CLEC) | 58(7%) | 6 | 2007-01-10 |
| T-Mobile USA | Wireless | 39(5%) | 2 | 2012-11-09 |
| AT&T Mobility (New Cingular Wireless PCS) | Wireless | 35(4%) | 2 | 2004-11-18 |
| MCImetro (Verizon Business) | Competitive / VoIP (CLEC) | 31(4%) | 1 | 2004-04-08 |
| Spok, INC. | Wireless | 31(4%) | 1 | — |
| Teleport Communications America, LLC | Competitive / VoIP (CLEC) | 28(4%) | 2 | — |
| Onvoy (Sinch) | Competitive / VoIP (CLEC) | 14(2%) | 3 | 2023-08-15 |
| American Messaging Services, LLC | Wireless | 11(1%) | 1 | — |
| Comcast (Xfinity Voice) | Competitive / VoIP (CLEC) | 7(1%) | 1 | 2007-08-24 |
| Electric Lightwave LLC dba Allstream | Competitive / VoIP (CLEC) | 3(0%) | 1 | — |
Largest rate centers (exchanges) by prefixes: Denver (735), Longmont (18), Fort Lupton (11), Deckers (5), Keenesburg (3), Allenspark–Lyons (2), Deer Trail (2), Georgetown (2), Hudson (2), Bennett (1). Source: NANPA Central Office Code Utilized Assignments (public, refreshed weekly).
What to do about calls from 303 numbers
Before you call back
- Medical & prescriptions is the top named complaint here. Don't confirm your Medicare or insurance number to a caller. Medicare won't cold-call you to sell braces, test kits or plans. Read about Medicare scam calls.
- Look up the full number above. A missed call from 303 with no voicemail is usually a robocall; anyone who needs you will leave a message.
- If it looks like a neighbor's number, it may be spoofed. See calls from your own area code.
- Block repeat callers: iPhone, Android, or your carrier's free filter (Verizon, AT&T, T-Mobile).
Report it in Colorado
- Unwanted sales calls and robocalls: donotcall.gov (FTC). Scams and fraud: ReportFraud.ftc.gov.
- Spoofing, texts and call-blocking problems: FCC consumer complaints.
- State complaints: Colorado Attorney General.
- Colorado is one of the states that maintains its own Do Not Call registry alongside the federal National Do Not Call Registry, so telemarketers calling Colorado numbers are expected to check both lists. Registering on the federal list at donotcall.gov is free and never expires; the state list is administered separately and may have its own registration process and renewal period.
Your FTC and FCC reports are published (without your name or number) in the datasets this page is built from. How to report unwanted calls.
Area code 303: questions answered from the data
Where is area code 303?
Area code 303 serves Denver and Longmont, Colorado, covering Denver County, Boulder County and Weld County and 4 more counties. It has been in service since 1947.
What time zone is area code 303 in?
Area code 303 is in the Mountain time zone (UTC−7, or UTC−6 during daylight saving time). The current local time is shown at the top of this page.
Which area codes overlay 303?
720 (in service 1998) and 983 (in service 2022) serve the same area as 303. New numbers there can be issued with any of these codes, and local calls need all 10 digits. A spoofed call can display any of them.
What are calls from 303 numbers usually about?
Since Jul 24, consumers filed 2,553 FTC Do Not Call complaints about 303 numbers. The most common named subject was medical & prescriptions: 12% of complaints, 79% of them recorded messages. Across all subjects, 69% of callers who answered the question said the call was a robocall.
When do 303 spam calls happen?
35% of the complaints that give a call time describe calls between 9am and 12pm, and 96% came on weekdays, most often on Tuesday. Times are as consumers reported them.
Are calls from 303 numbers really local?
Not necessarily. 82% of the FTC complaints about 303 numbers came from people whose own phone number also starts with 303, and 87% from Colorado. Calls that look local to the person receiving them are the signature of neighbor spoofing: robocallers display a number from your own area code because you're more likely to answer.
Are 303 robocalls increasing?
In the four weeks to Oct 20, consumers filed 734 FTC complaints about 303 numbers, 11% fewer than the four weeks before.
How do I report a 303 scam call in Colorado?
Report unwanted sales calls and robocalls to the FTC at donotcall.gov, and scams to ReportFraud.ftc.gov. The FCC takes complaints at consumercomplaints.fcc.gov. In Colorado, the Colorado Attorney General also handles consumer complaints about scam calls. Reports feed the public data this page is built from.
Overlay and nearby area codes
Sources: FTC Do Not Call complaints (unverified consumer reports), published every weekday and available here from Jul 24; FCC Consumer Complaint Data, public record, imported nightly; NANPA numbering records. A number appearing here means consumers reported calls that displayed it. Caller ID can be spoofed.