EST vs EDT
The two offsets of Eastern Time and when each one applies.
Basics · 1883 to today
History of Eastern Time
Eastern Time began as the railroads' clock at noon on November 18, 1883, became federal law on March 19, 1918, and has followed today's March–November daylight saving rule since 2007.
- Railroad standard time
- Nov 18, 1883
- In federal law since
- Mar 19, 1918
- Current DST rule
- Since 2007
- Eastern Time now
- --:-- ET
What time did East Coast cities keep before time zones?
Until 1883 each city set its clocks by its own sun. Local mean solar time runs 4 minutes earlier for every degree of longitude you travel west, because the Earth turns 360° in 24 hours (1,440 minutes). Nearby cities disagreed by many minutes, and each railroad ran on the time of its headquarters or a major city on its line, so one station could show several clocks.
The table measures each city against the 75th meridian, later the basis of Eastern Standard Time: Boston and Washington were almost 24 minutes apart.
| City | Longitude | Local time | vs New York |
|---|---|---|---|
| Boston | 71.06°W | 12:15:45 PM | 11 min 46 s ahead |
| New York | 74.01°W | 12:03:59 PM | — |
| Philadelphia | 75.16°W | 11:59:21 AM | 4 min 38 s behind |
| Washington | 77.01°W | 11:51:58 AM | 12 min 1 s behind |
How did the railroads create Eastern Time in 1883?
Canadian railway engineer Sandford Fleming proposed a worldwide system of 24 hourly zones in 1879. William F. Allen, secretary of the US railroads' General Time Convention, drew a practical version: each zone would keep the mean time of a meridian a whole number of hours from Greenwich, with changeover points at railroad division towns. The Convention adopted his plan in Chicago on October 11, 1883. The eastern section took the time of the 75th meridian, five hours behind Greenwich.
The switch came at noon on Sunday, November 18, 1883, remembered as the "Day of Two Noons". In New York, clocks reached 12:00 local time, ran on for almost four minutes, and were then set back to 12:00 on the new standard. A Boston clock on local time had to go back nearly 16 minutes; a Washington clock went forward about 8. It was a private railroad agreement; federal law ignored it for 35 years.
A year later, the International Meridian Conference in Washington (October 1884) chose Greenwich as the prime meridian by 22 votes to 1, with San Domingo against and France and Brazil abstaining. It also proposed a universal day counted from Greenwich midnight, a forerunner of today's UTC, but left local time to each nation.
When did Eastern Time become federal law?
The Standard Time Act (the Calder Act), signed by President Woodrow Wilson on March 19, 1918, wrote standard time zones into federal law and gave the Interstate Commerce Commission the job of drawing their limits (see why the Eastern Time Zone boundary is so irregular). The same act introduced the country's first daylight saving time as a wartime measure, beginning March 31, 1918. Clocks ran an hour ahead from the last Sunday in March to the last Sunday in October in 1918 and 1919.
After the war Congress voted to repeal the DST section. Wilson vetoed the repeal, and Congress overrode him on August 20, 1919. Standard time stayed federal, but summer time became a local option. New York City kept daylight time through the 1920s and 1930s while many nearby areas did not, so neighbours could be an hour apart all summer.
What were Eastern War Time and the 1945–1966 patchwork?
Year-round daylight time returned with the War Time Act of January 20, 1942. From February 9, 1942, the zone kept Eastern War Time (UTC−4) all year. After Japan's surrender the label changed to Eastern Peace Time on August 14, 1945, and standard time came back on September 30, 1945. EWT, EPT and other codes are decoded on our Eastern Time abbreviations page.
With no federal rule after 1945, states, counties and cities picked their own summer dates, or none. The best-known symptom: bus drivers on a 35-mile stretch of West Virginia Route 2 between Moundsville, West Virginia, and Steubenville, Ohio, had to reset their watches seven times.
How did the Uniform Time Act shape today's DST rules?
President Lyndon B. Johnson signed the Uniform Time Act on April 13, 1966. From 1967, any place that observed DST had to use the same dates: 2:00 AM on the last Sunday in April to 2:00 AM on the last Sunday in October. A state could opt out only as a whole (a 1972 amendment let split states exempt one zone), and oversight of the zones passed from the ICC to the new Department of Transportation. Later laws only moved the dates:
- 1974–75: after the oil embargo, an emergency law put the country on DST from January 6, 1974. After complaints about dark winter mornings, Congress restored standard time from October 27, 1974 to February 23, 1975.
- 1986: a law signed on July 8, 1986 moved the start to the first Sunday in April, effective 1987.
- 2005: the Energy Policy Act, signed August 8, 2005, created today's rule from 2007: second Sunday in March to first Sunday in November. The Energy Department's 2008 study put the electricity savings at about 0.03% of national use.
That is why Eastern Time now spends about 34 weeks a year on EDT and only 18 on Eastern Standard Time. Upcoming switch dates are listed on our daylight saving time guide.
What are the key dates in Eastern Time history?
Will Eastern Time switch to permanent daylight saving time?
Not yet. The Sunshine Protection Act would keep the country on summer time all year, with a state opt-out. A version passed the Senate by unanimous consent on March 15, 2022, then died in the House. The current bill, H.R. 139, passed the House 308–117 on July 14, 2026. As of November 2026 the Senate had not voted; the bill, like its Senate companion S. 29, sits with the Commerce Committee. Clocks fell back as usual on November 1, 2026, and the March 14, 2027 change is still law. By the National Conference of State Legislatures' count, 19 states have voted to adopt year-round DST if Congress allows it.
In Canada, Ontario's Time Amendment Act, 2020 would make daylight time permanent only if Quebec and New York do the same, and in late October 2026 Quebec's government said it intends to end the switch without yet choosing which time to keep.
The 1974 objection is easy to compute. On January 15, sunrise in New York is at 7:18 AM EST; on permanent DST it would be 8:18 AM, and in Detroit 8:59 AM. Compare the two offsets in EST vs EDT or see the live Eastern Time clock.
Frequently asked questions
Why is Eastern Time exactly five hours behind Greenwich?
The zone keeps the mean solar time of the 75th meridian west, and the Earth turns 15° per hour: 75 ÷ 15 = 5. Picking whole-hour meridians in 1883 is what made zones differ by exact hours; Greenwich became the world's zero line a year later.
Does the time zone database remember this history?
Yes. The IANA zone America/New_York starts with New York's local mean time, UTC−4:56:02, until noon on November 18, 1883, and it includes the city's own summer-time rules from the local-option years, so software can convert historical New York times correctly.
Was the United States the first country to use daylight saving time?
No. Germany and Austria-Hungary began on April 30, 1916, and the United Kingdom followed on May 21, 1916. The United States joined in 1918 under the Standard Time Act.
What would permanent daylight saving time mean for EST?
Eastern clocks would stay at UTC−4, today's EDT offset, all year. In winter New York would then share a clock with Halifax on Atlantic Standard Time, and the seasonal EST/EDT distinction would disappear.
Did Canada follow the same rule changes?
Ontario and Quebec set their own time by provincial law but matched the US change for 2007 (Quebec through its Legal Time Act, in force January 1, 2007), so Toronto and Montreal still switch on the same nights as New York.
Explore
Daylight saving time
Every spring-forward and fall-back date through 2030.
Time zone boundaries
How the 1918 zones became today's county-by-county line.
Abbreviations
ET, EST, EDT, EWT, EPT and the military letters decoded.
Eastern Standard Time
UTC−5, the winter offset that dates back to 1883.