Area code
203
203 is a United States area code. Under the North American Numbering Plan it belongs to Connecticut, which has 4 area codes in total.
Validate a number in 203
Paste a full number and the tool checks it against the numbering plan. It returns the standard formats, the line type the plan assigns and the area code region.
Digits with or without punctuation work. Numbers outside the US are read with the +country code.
Area code 203 at a glance
NANPA lists 784 central office codes (prefixes) in use in area code 203, held by 21 holders across 33 rate centers.
| Fact | Value |
|---|---|
| In service since | 1947-01-01 |
| Time zone | Eastern (E) |
| Assigned overlays | 475 (2009-12-12) |
| Prefixes in use | 784 |
| Pooled prefixes | 473 (60%) |
| Rate centers | 33 |
| Companies holding prefixes | 21 |
| Assignment dates on file | 2001-01-03 to 2024-09-18 (126 prefixes) |
| ZIP codes in its places | 120 |
Rate centers in area code 203
| Rate center | Prefixes | Share |
|---|---|---|
| NEW HAVEN | 145 | 18% |
| STAMFORD | 97 | 12% |
| BRIDGEPORT | 94 | 12% |
| NORWALK | 60 | 8% |
| DANBURY | 54 | 7% |
| WATERBURY | 52 | 7% |
| GREENWICH | 27 | 3% |
| MERIDEN | 24 | 3% |
| 25 other rate centers | 231 | 29% |
Who holds the prefixes in 203
Frontier Comm Of CT holds the most prefixes, 338 (43%). 60% of the prefixes are pooled, which means their thousands-blocks can belong to different companies.
| Holder | Prefixes | Share |
|---|---|---|
| Frontier Comm Of CT | 338 | 43% |
| Verizon Wireless | 61 | 8% |
| New Cingular Wireless PCS | 52 | 7% |
| Omnipoint Communications | 47 | 6% |
| Level 3 Communications | 41 | 5% |
| Mcimetro Access Transmission Services | 41 | 5% |
| 15 other carriers | 204 | 26% |
A prefix holder is the company a code was assigned to, not necessarily a number's current carrier, because numbers can be ported to another company. Find which carrier a number is on, or browse the prefix holders.
History of area code 203
- 1947-01-01 Area code 203 went into service.
- 1995-08-28 Area code 860 went into service and names 203 as its parent.
- 2009-12-12 Area code 475 went into service as an overlay in the same area as 203.
Area codes nearest to 203
Distance is measured between the centers of the ZIP code places each area code serves, so it is a rough guide.
Overlay codes in the same area
ZIP codes in area code 203
120 ZIP codes fall in places that have a rate center in this area code.
| Place | ZIP codes |
|---|---|
| New Haven, CT | 28 |
| Stamford, CT | 17 |
| Waterbury, CT | 16 |
A ZIP code and an area code are unrelated systems. A ZIP code can sit in more than one area code, and an area code spans many ZIP codes.
Complaints on file for 203 numbers
4,791 FCC complaints are on file for 3,367 numbers in 203, most often filed as "Unwanted Calls". These are unverified consumer reports.
| Year of latest complaint | Numbers |
|---|---|
| 2023 | 163 |
| 2024 | 163 |
| 2025 | 102 |
Other area codes in Connecticut
Connecticut is one state with 4 area codes in the NANPA table. 203 is one of them.
Next to 203 in the numbering table
These are the codes just before and after 203 when all are sorted by number. They are neighbours on the list, not necessarily on the map.
What the area code does and does not tell you
A number that starts with 203 was first assigned in Connecticut. That is a fact about where the number began, and it is a useful hint when you check a form entry, for example a billing address in Connecticut next to a 203 phone number.
It does not show where the person is today. A number stays with its owner after a move or a change of provider (number portability), and mobile numbers travel with the handset. The area code also cannot tell you whether the line is active, who the carrier is, or whether the number is mobile or fixed: the plan shares those ranges. Read more about the area code, the numbering plan and line type.
Check numbers in bulk with the API
| Product | Credits | Docs |
|---|---|---|
| Phone Numbering-Plan Validation | 1 credit per valid number | API docs |
| Phone Intelligence (carrier and line status) | 1 credit per check (invalid numbers outside the US and Canada are free) | Product page |
Questions about area code 203
Where is area code 203?
NANPA assigns area code 203 to Connecticut, United States.
In which state does area code 203 sit?
Connecticut. 203 is one of 4 area codes the NANPA table assigns to the state.
Which places does area code 203 cover?
The places with the most ZIP codes among the rate centers in 203 are New Haven, CT, Stamford, CT and Waterbury, CT. The rate center list on this page shows all of them.
Who owns area code 203?
NANPA assigns area codes. Within 203, Frontier Comm Of CT holds the most prefixes, 338 prefixes or 43%.
Which time zone does 203 use?
The NANPA NPA report lists the time zone for 203 as Eastern (E).
What year did 203 enter service?
The NANPA NPA report gives an in-service date of 1947-01-01, so 203 has been in use since 1947.
Does area code 203 have an overlay?
Yes. 475 (in service 2009-12-12) shares the same area with 203, so numbers from all of them are local to each other.
Which area codes are nearest to 203?
The area codes closest to 203, measured between the centers of the ZIP code places they serve, are 934 (about 31 miles), 631 (about 32 miles), 516 (about 35 miles), 914 (about 38 miles) and 860 (about 41 miles).
How many prefixes does area code 203 have?
NANPA's report dated 2026-10-17 lists 784 prefixes in service in 203, spread over 33 rate centers and 21 holders.
Are there complaints about 203 numbers?
The FCC data on file has 4,791 complaints for 3,367 numbers in 203. They are unverified consumer reports. A number with no complaints on file is not proven safe.
Area code assignments: North American Numbering Plan Administrator NPA report, file dated 10/17/2026, retrieved 2026-10-17. Source file. New codes are assigned several times a year. Prefixes, rate centers, holders, time zone, in-service date and overlays: NANPA central office code report dated 2026-10-17 and NPA report dated 2026-10-18. Complaints: FCC consumer complaints open data, fetched 2026-10-17. ZIP code places: Postal code places and coordinates: GeoNames (geonames.org), licensed CC BY 4.0.