Basics · Geography of time

Why the Eastern Time Zone boundary is so irregular

Because it is a legal line, not a solar one: the US Department of Transportation draws it county by county in 49 CFR Part 71 for the "convenience of commerce", so Eastern Time reaches past 89°W although its reference meridian is 75°W.

Reference meridian
75°W
Ideal solar band
82.5°W – 67.5°W
Eastern Time now
--:-- ET
Central Time now
--:-- CT

What is the difference between a solar and a legal time zone?

In theory each zone is a band 15° wide centred on a meridian divisible by 15. Eastern Time's centre is 75°W, so a purely solar zone would run from 82.5°W to 67.5°W, and local mean noon would fall within 30 minutes of 12:00 everywhere inside it.

The legal zone is different. Under 49 CFR §71.4, the Eastern zone is the part of the United States west of 67°30′W, plus all of Maine, and east of the line described in §71.5. The eastern edge matches the solar band; the western edge does not. Detroit (83.0°W), Atlanta (84.4°W) and Indianapolis (86.2°W) all lie west of 82.5°W, in the solar Central zone.

The bulge exists because commerce pulls west. When the railroads drew the first zones in 1883, the Eastern–Central changeover points were Detroit, Buffalo, Pittsburgh, Atlanta and Charleston. Since then place after place has chosen the clock of New York and Washington; our history of Eastern Time shows how that line became law.

The solar UTC−5 band runs from 82.5°W to 67.5°W, but legal Eastern Time stretches from about 89.3°W at Ontonagon, Michigan, to 64.5°W at Gaspé, Quebec Solar UTC−5 band Legal Eastern Time Detroit 83.0°W New York 74.0°W Gaspé 64.5°W Ontonagon 89.3°W Lubec 67.0°W 95°W90°W85°W80°W75°W70°W65°W60°W
Legal Eastern Time extends about 7° past the western edge of its solar band.

Who decides where the Eastern Time Zone ends?

The Standard Time Act of 1918 gave the job to the Interstate Commerce Commission, because railroads were the reason zones existed. After the Uniform Time Act of 1966 and the law creating the Department of Transportation, that power passed to DOT, which has administered the boundaries since 1967. The statute sets one test: a boundary must respect "the convenience of commerce and the existing junction points and division points of common carriers" (15 U.S.C. 261). DOT reads commerce broadly: where residents work, shop and get medical care, which broadcasters they receive, and where the nearest airport, rail or bus hub is.

A state cannot move itself between zones. Changes go through a rulemaking:

  1. The highest elected officials of the area petition DOT: for a county, usually the board of commissioners; for a state, the governor or legislature.
  2. The petition documents why the change suits the convenience of commerce, with business surveys, commuting data and media markets.
  3. DOT publishes a proposed rule, takes public comments and usually holds a hearing in the area.
  4. A final rule amends 49 CFR Part 71, normally taking effect at the next switch between daylight and standard time.

Petitions that fail the commerce test are denied, but a county may try again if circumstances change.

Where does the Eastern–Central line actually run?

  • Michigan: the line crosses the Upper Peninsula on county lines, leaving Gogebic, Iron, Dickinson and Menominee counties on Central Time with Wisconsin, then runs down the middle of Lake Michigan. Marquette and Ontonagon are Eastern. Michigan time zones
  • Indiana: 12 of 92 counties use Central Time, six near Chicago and six near Evansville. When the state began statewide DST on April 2, 2006, eight counties moved to Central; six of them returned to Eastern within two years. Indiana time zones
  • Kentucky: the line follows the western edges of a chain of Eastern counties from Meade and Hardin south to Pulaski and Wayne, so Louisville and Lexington are Eastern while Bowling Green, Owensboro and Paducah are Central. Kentucky time zones
  • Tennessee: East Tennessee, bounded by Scott, Morgan, Roane, Rhea and Hamilton counties, is Eastern, with Knoxville and Chattanooga; Nashville and Memphis are Central.
  • Georgia–Alabama: here the legal line is the state border. In practice Phenix City and nearby Alabama towns such as Lanett, Valley and Smiths Station keep Eastern Time unofficially, because so many residents work across the Chattahoochee in Columbus, Georgia.
  • Florida: the line follows the Apalachicola River below Jim Woodruff Dam, then the Jackson River and the Intracoastal Waterway to Gulf County's west line. That splits Gulf County: Port St. Joe is Eastern, Wewahitchka Central. Florida time zones
  • Eastern Time
  • Central Time
  • 75°W solar meridian

How does Canada draw its Eastern Time boundary?

Canadian time is provincial law. Ontario's Time Act puts the province on Eastern Time east of 90°W and on Central Time west of it, with long-standing exceptions: Atikokan has kept UTC−5 all year since at least 1952, and Pickle Lake does the same. On November 1, 2026, Ontario Regulation 333/26 put all of Ontario west of 90°W on UTC−5 year-round, to stay aligned with Manitoba, which ended its clock changes that weekend. From November to March, Kenora and Dryden now show the same time as Thunder Bay and Toronto on EST; from March to November they will be an hour behind EDT. Thunder Bay, just east of the meridian, still switches with Toronto.

Quebec's legal time is Eastern west of 63°W. The Lower North Shore around Blanc-Sablon keeps Atlantic Standard Time (UTC−4) all year, while the Magdalen Islands and the Listuguj reserve follow Atlantic Time with DST, like neighbouring New Brunswick.

How late is solar noon at the western edge of Eastern Time?

Solar noon and sunrise, computed for each place (accurate to about ±2 minutes)
PlaceLongitudeSolar noon, Jun 21, 2026 (EDT)Solar noon, Dec 21, 2026 (EST)Sunrise, Dec 21, 2026 (EST)
Gaspé, QC64.49°W12:20 PM11:16 AM7:09 AM
Lubec, ME66.98°W12:30 PM11:26 AM7:03 AM
New York, NY74.01°W12:58 PM11:54 AM7:17 AM
Detroit, MI83.05°W1:34 PM12:30 PM7:58 AM
Columbus, GA84.99°W1:42 PM12:38 PM7:38 AM
Terre Haute, IN87.41°W1:52 PM12:48 PM8:06 AM
Ontonagon, MI89.31°W1:59 PM12:55 PM8:40 AM
Thunder Bay, ON89.25°W1:59 PM12:55 PM8:46 AM
Ironwood, MI (Central)90.17°W1:03 PM CDT11:59 AM CST7:41 AM CST

Gaspé and Ontonagon share a clock but sit 25° of longitude apart, so the sun peaks 1 hour 40 minutes later in Ontonagon: 1:59 PM EDT at the June solstice, with sunset around 9:56 PM. In December, sunrise there comes around 8:40 AM. Ironwood, about 50 miles southwest on Central Time, sees the same sun only 3–4 minutes later, yet its clocks read almost an hour earlier. Permanent daylight time would push Ontonagon's December sunrise to about 9:40 AM. To see what the gap between EST and EDT means where you are, check today's sun times on the live Eastern Time clock.

Frequently asked questions

Is the Eastern Time boundary the same as a state line?

Only in places. It follows the Georgia–Alabama and Florida–Georgia state lines and Michigan's water boundary in Lake Michigan; elsewhere it runs along county lines, the Apalachicola River and the Intracoastal Waterway.

Which zone applies to a town that sits right on the boundary?

Central Time. 49 CFR §71.5(h) states that all municipalities located on the Eastern–Central boundary line are in the Central zone.

Where is the eastern edge of the Eastern Time Zone?

In the United States, 49 CFR §71.4 sets it at 67°30′W but includes all of Maine, so Lubec and Eastport keep Eastern Time while New Brunswick, across the border, is an hour ahead on Atlantic Time. Puerto Rico and the US Virgin Islands use Atlantic Standard Time.

Which IANA zone should software use for places near the line?

Choose by location, not by state. Besides America/New_York, the tz database has zones such as America/Detroit, America/Indiana/Indianapolis, America/Kentucky/Louisville and America/Menominee (the Central counties of Michigan's Upper Peninsula), because their clock histories differ.

How can I tell which time zone a specific town uses?

Find its county in 49 CFR §71.5 or on the time zone map, then check local practice: a few border towns, such as Phenix City, Alabama, follow a neighbouring city's clock unofficially.

Explore

EST vs EDT

The two offsets every place inside the boundary switches between.