Area Code 303

About Area Code 303

Area code 303 is a geographic telephone area code assigned to Denver, Colorado. It operates in the Mountain time zone and was first introduced in 1947. Original NANP code. Denver metro. Overlay 720 (1998).

Within Colorado, area code 303 shares numbering capacity with 3 other area codes. The state's 5,839,926-person population (2023 Census Bureau estimate) is served by a combined 4 active codes, with 303 primarily responsible for the Denver region. Colorado's state capital is Denver, and its largest city is Denver.

When you receive a call from a 303 number on your Caller ID, the call originated from a phone number assigned to the 303 area code — but be aware that Local Number Portability (in effect since 2003) means the caller could be physically located anywhere in the US or Canada. Area code 303 only confirms where the number was originally assigned.

Where is the 303 area code located?

Area code 303 is assigned to Denver, Colorado, in the Mountain time zone. The state of Colorado uses 4 active area codes, and 303 is one of them. Calls placed from the 303 area code originate from numbers assigned by NANPA — the North American Numbering Plan Administrator — and the 303 prefix appears on Caller ID for both landline and wireless calls placed from this region.

The Mountain time zone observes Daylight Saving Time, shifting from UTC-7 to UTC-6 in summer. The local time shown above is always current, so you can quickly check whether it's a reasonable hour to call back.

What cities and counties use the 303 area code?

The 303 area code serves 9 notable cities, listed below in order of population. The largest city in the 303 territory is Denver (715,522 residents in Denver County).

• Denver, CO — 715,522 residents (29.5% of 303 numbers)
• Colorado Springs, CO — 486,248 residents (20.1% of 303 numbers)
• Aurora, CO — 399,524 residents (16.5% of 303 numbers)
• Fort Collins, CO — 171,690 residents (7.1% of 303 numbers)
• Lakewood, CO — 156,706 residents (6.5% of 303 numbers)
• Thornton, CO — 142,442 residents (5.9% of 303 numbers)
• Arvada, CO — 123,436 residents (5.1% of 303 numbers)
• Westminster, CO — 115,625 residents (4.8% of 303 numbers)
• Pueblo, CO — 112,121 residents (4.6% of 303 numbers)

Phone number format in area code 303

All phone numbers within area code 303 follow the standard North American 10-digit format:(303) NXX-XXXX. The NXX is the central office prefix (also called an "exchange") and XXXX is the subscriber line number. For long-distance calls within the NANP, dial 1 + 303 + NXX + XXXX. From outside North America, dial your country's international access code, then 1 (the NANP country code), then the 10-digit number.

If you need to verify whether a specific 303 number is wireless, landline, or VoIP, you can use our reverse phone lookup tool. Be aware that number portability means the area code no longer guarantees the caller's physical location — only where the number was first assigned.

History of area code 303

Original NANP code. Denver metro. Overlay 720 (1998).

The original 86 area codes were assigned by AT&T and Bell Labs in 1947 as part of the North American Numbering Plan. At the time, rotary-dial phones meant codes with lower digits (like 212 for NYC, 213 for LA, 312 for Chicago) were given to the largest cities because they took less time to dial. Today's area code assignments still reflect those early choices, even though touch-tone and cell phones made the original reason obsolete.

Is the 303 area code safe to answer?

Area code 303 itself is a normal geographic code with no elevated spam risk. That said, scammers can spoof any area code — including 303 — so if you don't recognize the full number, let it go to voicemail and verify the caller's identity before calling back.