One of the most diverse cities in the country, Gaithersburg is a fast-growing Montgomery County suburb of Washington, D.C., home to the National Institute of Standards and Technology. It is covered by the 301 code and its overlay. This guide breaks down Gaithersburg’s 301 and 240 codes, the required 10-digit dialing, major ZIP codes, and local scam warnings.
Gaithersburg Area Codes at a Glance
| Detail | Information |
|---|---|
| Primary Area Code(s) | 301 |
| Overlay Area Code(s) | 240 |
| Time Zone | Eastern Time (ET) – EST / EDT |
| Major County | Montgomery County |
| Region | DC Suburbs (Montgomery County) |
| Dialing Format | 10-digit dialing required |
Area Code Breakdown & Regional Mapping
301 – Western MD & DC Suburbs Code
Area code 301 is one of the original 1947 codes and covers the Washington, D.C. suburbs and Western Maryland, including Gaithersburg, Rockville, and Bowie. It is Gaithersburg’s primary code within Montgomery County.
240 – Western MD & DC Suburbs Overlay
Area code 240 is the 1997 overlay for the 301 region, sharing the same DC-suburbs and western-Maryland geography. Many newer Gaithersburg lines carry a 240 prefix, fully local to existing 301 numbers.
Neighborhoods & Local Coverage
Gaithersburg’s 301/240 codes cover a city anchored by its historic Olde Towne district around the old railroad station, alongside the acclaimed new-urbanist community of Kentlands with its walkable town center. The Rio (formerly Washingtonian Center) waterfront district draws shoppers and diners to Lake Washington.
Beyond those hubs, the same codes reach the Lakelands and Quince Orchard neighborhoods, the sprawling Montgomery Village community to the north, and the NIST research campus. As part of the DC suburbs, Gaithersburg shares the 301/240 codes with neighboring Rockville and the rest of Montgomery County.
Local Dialing Rules & International Format
Gaithersburg and the 301 region have required 10-digit dialing since the 240 overlay launched — always dial the area code plus the 7-digit number. Baltimore to the northeast uses a separate complex, 410/443/667.
Gaithersburg is in the Eastern Time Zone (EST/EDT), like all of Maryland. To call the city from outside the United States, dial your country’s exit code, then the U.S. country code +1, followed by the 10-digit number (for example, +1 301 XXX-XXXX). From inside the U.S. and Canada, simply dial 1 before the 10-digit number for long-distance calls.
Major ZIP Codes Covered
The 301 service area spans many of Gaithersburg’s core ZIP codes, including 20877, 20878, 20879, 20882, and 20886.
Spam & Scam Call Warnings in Gaithersburg
Gaithersburg residents report neighbor-spoofing robocalls faking a local 301 prefix, plus fake utility-shutoff threats from callers posing as Pepco. Bilingual robocalls also target the city’s large immigrant communities.
| Scam Type | What to Watch For |
|---|---|
| Neighbor Spoofing | Calls that mimic a local 301 prefix to look familiar. |
| Utility / Toll Scams | Threats to shut off power or demand toll payment via gift cards. |
| IRS / Government | Robocalls claiming legal action — agencies never call to demand instant payment. |
Red flag: Any caller who pressures you to pay immediately with gift cards, wire transfers, or cryptocurrency is almost certainly running a scam. Hang up and verify through an official number.
↑ See the complete list of All US Area Codes by State for every code across the country.
Nearby & Related Maryland Cities
Frequently Asked Questions
What area code is Gaithersburg, MD?
Gaithersburg uses area code 301 and its overlay 240, shared across the DC suburbs and Western Maryland.
Does Gaithersburg have the same area code as Rockville?
Yes. Gaithersburg, Rockville, and the rest of Montgomery County all use 301/240.
Do I need to dial 10 digits in Gaithersburg?
Yes. With the 240 overlay active, all local calls in the 301 region require 10-digit dialing.
What time zone is Gaithersburg in?
Gaithersburg observes Eastern Time (EST/EDT), like all of Maryland.
Stay Safe & Explore More
- Verify an unknown caller in our Scam Alerts directory.
- Comparing nationwide numbers? See our Toll-Free Numbers guides.