The 857 area code is an overlay serving Boston and Cambridge, Massachusetts, layered over the iconic 617 code. Introduced in 2001 to supply new phone numbers for the Greater Boston core, 857 covers the exact same territory as 617. If an 857 number has appeared on your caller ID, this guide explains where it comes from, how to dial it, and how to stay safe from spoofed calls.
Quick Summary: Area Code 857 at a Glance
| Detail | Information |
|---|---|
| Area Code | 857 |
| State | Massachusetts (MA) |
| Major Cities | Boston, Cambridge, Somerville, Brookline |
| Time Zone | Eastern Time (ET) |
| Country Code | +1 (USA) |
| Overlay Codes | 617 (co-located) |
Geographic Coverage & Major Cities
Area code 857 covers the urban core of Greater Boston, including the city of Boston, Cambridge, and the inner communities of Suffolk and Middlesex counties. Because it is an overlay, it shares the identical footprint of the 617 area code rather than covering a separate zone.
- Boston – the capital and largest city in Massachusetts
- Cambridge – home to Harvard University and MIT
- Somerville & Brookline – dense inner communities
- Newton & Quincy – established Greater Boston cities
As the newer code over Boston, 857 numbers are common among lines set up after the original 617 numbers grew scarce.
A Brief History of Area Code 857
Area code 857 was activated in 2001 as an all-services overlay on the 617 region. The 617 code is one of the original 1947 codes. An overlay adds a second area code across the same geographic area, so existing 617 customers kept their numbers while new lines could be assigned either code, under mandatory 10-digit dialing.
Time Zone & Best Time to Call
Numbers in the 857 area code use Eastern Time (ET). The region observes Daylight Saving Time, shifting from EST (UTC-5) to EDT (UTC-4) between March and November each year.
How to Dial Phone Numbers in Area Code 857
Because 857 shares its region under an overlay, the area requires 10-digit dialing on every call.
Calling within the United States or Canada
- 10-digit dialing: Include the area code – 857-XXX-XXXX.
- 11-digit dialing: You can also dial 1-857-XXX-XXXX; the leading 1 is the NANP country code.
Calling from outside the United States
- Format: [exit code] + 1 + 857 + XXX + XXXX
- From the UK, Europe, or most of Asia/Africa: 00 1 857 XXX XXXX
- From any mobile phone worldwide: +1 857 XXX XXXX
Is Area Code 857 a Scam? Safety & Protection Tips
Area code 857 is a legitimate Massachusetts area code – a call from it is not fraudulent by default. However, scammers frequently spoof local codes like 857, faking the caller ID so their number appears to come from a trusted local line. Neighbor spoofing, which mimics the first six digits of your own number, is especially common.
Common scam tactics linked to this region
| Scam type | What to watch for |
|---|---|
| Government impersonation | Callers posing as the IRS or SSA threatening arrest or fines |
| Bank & card fraud alerts | Claims of suspicious activity seeking your account details |
| Student & scholarship scams | Fake tuition or financial-aid calls targeting Harvard, MIT, or BU students |
| Utility shut-off threats | Fake Eversource or National Grid disconnection demands |
How to report, block, and look up 857 callers
- Never share personal or financial details with an unexpected caller, however urgent they sound.
- Block the number using your phone’s built-in call-blocking feature or a reputable call-screening app.
- Look up the number with a trusted reverse phone lookup before returning any call.
- Report it to the FTC at reportfraud.ftc.gov and register at DoNotCall.gov.
Nearby & Related Area Codes in Massachusetts
Area code 857 shares and borders several other Massachusetts codes:
- 617 – the original Boston and Cambridge code that 857 overlays (see our 617 area code guide)
- 781 & 339 – the inner Boston suburbs ringing the city (see our 781 area code guide)
- 508 & 774 – central and southeastern Massachusetts (see our 508 area code guide)
- 978 & 351 – the Merrimack Valley and northeastern Massachusetts (see our 978 area code guide)
Explore more codes across the state on our Massachusetts area codes hub, or browse every prefix in our US area codes directory.
↑ 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 Massachusetts:
- New Hampshire – area code 603
- Vermont – area code 802
- New York – area code 212
- Connecticut – area code 203
- Rhode Island – area code 401
Frequently Asked Questions About Area Code 857
Where is the 857 area code located?
Area code 857 covers Boston and Cambridge, Massachusetts, as an overlay of the 617 code. It operates on Eastern Time.
What is the difference between 857 and 617?
There is no geographic difference. 857 overlays the exact same Boston and Cambridge territory as 617; it was added in 2001 simply to supply more phone numbers.
Is 857 a landline or cell phone area code?
Both. Area code 857 serves landlines, mobile phones, and VoIP numbers throughout Greater Boston.
Should I answer a call from an unknown 857 number?
If you are not expecting the call, let it go to voicemail. Legitimate callers leave a message, while spoofed or robocall numbers usually will not. Verify any unfamiliar number with a reverse lookup before calling back.
Related 857 Guides
- Is a 857 call safe? Read Is area code 857 a scam? Spam & safety guide.
- Local coverage: see the Boston area code guide.
- Worried about spam or robocalls? Browse our Scam Alerts directory.