At noon on 18 November 1883, telegraph signals from the US Naval Observatory told every railroad in the United States and Canada to reset their clocks. In towns across the country, people gathered in squares holding pocket watches, waiting for the operator to announce the moment. Some places got two noons that day: one in old local solar time, one in the new standard. The railroads had not asked Congress. They acted because the alternative was more collisions.
Before that Sunday, American time was a local affair. A city set its clocks by the sun. When the sun hit its highest point, it was noon. That worked until railroads stitched the continent together. By 1883, more than 100 different local times governed train schedules. A trip from New York to Chicago meant resetting a watch dozens of times. Worse, schedules written in incompatible times caused near-misses and wrecks on busy corridors. The railroads drew four zones and imposed them overnight: Eastern, Central, Mountain, Pacific. Within months, most cities had adopted the system voluntarily. The following year, the International Meridian Conference in Washington, DC, built worldwide time zones on the same principle.
Congress catches up, 1918
The federal government took 35 years to write the railroad zones into law. On 19 March 1918, President Woodrow Wilson signed the Standard Time Act, also called the Calder Act. The law did two things. It codified the four zones. And it introduced daylight saving time, a wartime fuel-saving measure. Germany had adopted DST in 1916; the United States followed. The Interstate Commerce Commission got authority over zone boundaries.
Farmers hated DST immediately. Cows do not read clocks. Morning milking schedules shifted against the sun. Congress repealed DST on 20 August 1919, overriding Wilson's veto. Standard time stayed. DST became a local free-for-all.
War Time, 1942 to 1945
President Franklin D. Roosevelt reinstated year-round DST on 9 February 1942. The country ran on Eastern War Time, Central War Time, Mountain War Time, and Pacific War Time for more than three years. When the war ended, Congress dropped War Time and left DST to states and cities again.
The chaos years, 1945 to 1966
Anarchy followed. States, counties, and individual towns set their own DST start and end dates, or ignored it entirely. In 1965, Iowa alone had 23 different DST start dates. A 30-minute drive could cross three different clock rules. Broadcasters, airlines, and bus companies flooded the Interstate Commerce Commission with complaints.
The Uniform Time Act of 1966
Congress imposed order with the Uniform Time Act of 1966, signed by President Lyndon Johnson. It set one DST window nationwide: last Sunday in April to last Sunday in October. It also gave states an escape hatch. A state could opt out of DST entirely by passing a state law. Arizona and Hawaii took that option quickly. The law moved time zone authority from the Interstate Commerce Commission to the new Department of Transportation, which still holds it.
The 1974 experiment that failed
The OPEC oil embargo pushed Congress to try year-round DST again. President Richard Nixon signed the Emergency Daylight Saving Time Energy Conservation Act on 6 January 1974, starting a two-year trial. It collapsed in months. Children waited for school buses in winter darkness. After a Florida child was killed at a dark bus stop in February 1974, public opinion turned hard. Congress repealed the experiment in October 1974. By April 1975, the country was back on winter standard time.
DST expands, 1986 and 2007
President Ronald Reagan signed a law in 1986 moving the DST start from the last Sunday in April to the first Sunday in April, adding about three weeks.
The Energy Policy Act of 2005, signed by President George W. Bush, pushed DST further. Starting in 2007, DST runs from the second Sunday in March to the first Sunday in November. That made DST the longest stretch in US history.
Alaska consolidates, 1983
Until 1983, Alaska operated four time zones. The state spans enough longitude to make that logical but impractical. Scheduling anything (legislative sessions, fishing openings, flights) was a mess. Alaska consolidated to two zones in 1983: Alaska Time (UTC−9) for most of the state and Hawaii-Aleutian Time (UTC−10) for the western Aleutian Islands.
Indiana standardizes, 2006
No state tangled its clocks like Indiana. Before 2006, 80 counties observed DST, 17 did not, and five counties in the northwest and southwest corners followed Central Time while the rest used Eastern Time. A summer drive across the state could mean multiple clock changes. Business groups argued the confusion cost millions. The legislature voted in 2005 to observe DST statewide, effective April 2006. Indiana remains split between Eastern and Central Time, but the DST rules are now uniform.
How DST works now
Clocks spring forward on the second Sunday in March at 02:00 local time and fall back on the first Sunday in November at 02:00 local time. The Department of Transportation oversees boundaries. States may opt out of DST entirely by passing a state law. They cannot adopt permanent DST without an act of Congress.
Most of Arizona stays on Mountain Standard Time year-round. The Navajo Nation, inside Arizona, observes DST. The Hopi Reservation, inside the Navajo Nation, does not. The result is a DST doughnut. Hawaii stays on Hawaii Standard Time year-round. The US territories (Puerto Rico, Guam, the US Virgin Islands, American Samoa, the Northern Mariana Islands) do not observe DST either.
The Sunshine Protection Act, which would make DST permanent nationwide, passed the Senate in March 2022 but stalled in the House. At least 19 states have passed legislation or resolutions for permanent DST, all contingent on Congressional approval. Florida was first, in 2018. The debate turns on health (circadian disruption from the spring switch versus more evening daylight), child safety during dark school mornings, and commerce.
Washington, DC, right now
Washington sits in the Eastern Time Zone (America/New_York). In January, the city runs on Eastern Standard Time, UTC−5. In July, it runs on Eastern Daylight Time, UTC−4.
Time differences in winter
On 15 January 2026, relative to Washington (EST), Los Angeles is 3 hours behind, Chicago is 1 hour behind, London is 5 hours ahead, Paris is 6 hours ahead, Johannesburg is 7 hours ahead, Dubai is 9 hours ahead, Mumbai is 10.5 hours ahead, Singapore is 13 hours ahead, Tokyo is 14 hours ahead, Sydney is 16 hours ahead, and São Paulo is 2 hours ahead.
Time differences in summer
On 15 July 2026, relative to Washington (EDT), Los Angeles remains 3 hours behind, Chicago stays 1 hour behind, London is 5 hours ahead, Paris is 6 hours ahead, Johannesburg is 6 hours ahead, Dubai is 8 hours ahead, Mumbai is 9.5 hours ahead, Singapore is 12 hours ahead, Tokyo is 13 hours ahead, Sydney is 14 hours ahead, and São Paulo is 1 hour ahead. The shifts happen because some cities observe DST on different schedules, or not at all.
Daylight across the year
Washington's daylight swings hard across the year. On the March equinox (20 March 2026), sunrise is at 07:13 and sunset at 19:19, giving 12 hours 6 minutes of daylight. On the June solstice (21 June 2026), sunrise is at 05:42 and sunset at 20:36: 14 hours 54 minutes of daylight. On the September equinox (22 September 2026), sunrise is at 06:54 and sunset at 19:07: 12 hours 13 minutes. On the December solstice (21 December 2026), sunrise is at 07:22 and sunset at 16:49: just 9 hours 26 minutes.
Upcoming clock changes in Washington
- Sunday 8 March 2026 at 02:00 local: clocks go forward 60 minutes to 03:00. EST (UTC−5) becomes EDT (UTC−4).
- Sunday 1 November 2026 at 02:00 local: clocks go back 60 minutes to 01:00. EDT (UTC−4) becomes EST (UTC−5).
- Sunday 14 March 2027 at 02:00 local: clocks go forward 60 minutes to 03:00. EST (UTC−5) becomes EDT (UTC−4).
- Sunday 7 November 2027 at 02:00 local: clocks go back 60 minutes to 01:00. EDT (UTC−4) becomes EST (UTC−5).
US public holidays, 2026 and 2027
The federal holiday calendar shapes business hours, travel, and trading days.
2026 holidays
- New Year's Day: Thursday 1 January
- Martin Luther King Jr. Day: Monday 19 January
- Washington's Birthday: Monday 16 February
- Memorial Day: Monday 25 May
- Juneteenth National Independence Day: Friday 19 June
- Independence Day (observed): Friday 3 July
- Independence Day: Saturday 4 July
- Labor Day: Monday 7 September
- Columbus Day: Monday 12 October
- Veterans Day: Wednesday 11 November
- Thanksgiving Day: Thursday 26 November
- Christmas Day: Friday 25 December
2027 holidays
- New Year's Day: Friday 1 January
- Martin Luther King Jr. Day: Monday 18 January
- Washington's Birthday: Monday 15 February
- Memorial Day: Monday 31 May
- Juneteenth National Independence Day (observed): Friday 18 June
- Juneteenth National Independence Day: Saturday 19 June
- Independence Day: Sunday 4 July
- Independence Day (observed): Monday 5 July
- Labor Day: Monday 6 September
- Columbus Day: Monday 11 October
- Veterans Day: Thursday 11 November
- Thanksgiving Day: Thursday 25 November
- Christmas Day (observed): Friday 24 December
- Christmas Day: Saturday 25 December
- New Year's Day (observed): Friday 31 December
How time zones shape daily life
Business and government hours
US business hours typically run 9:00 AM to 5:00 PM local time, Monday through Friday. Financial markets follow Eastern Time. The New York Stock Exchange and NASDAQ open at 9:30 AM ET and close at 4:00 PM ET, which means West Coast traders start at 6:30 AM PT. Government offices generally operate 8:00 AM or 9:00 AM to 4:30 PM or 5:00 PM local time. Federal offices align with Washington hours for national coordination.
Retail and shopping
Retail hours are wider. Large stores and malls often run 10:00 AM to 9:00 PM. Supermarkets may open at 7:00 AM and close at 10:00 PM, or stay open 24 hours. Sunday hours can be shorter in some areas.
School start times and the DST debate
School start times matter in the DST debate. Elementary schools typically begin between 8:00 AM and 8:30 AM. Middle and high schools often start earlier, between 7:15 AM and 8:00 AM. After the spring-forward switch, students walk to school in darker mornings for several weeks, a recurring argument against permanent DST.
Meal times
Breakfast runs 6:30 AM to 9:00 AM. Lunch peaks at noon, with business lunches often scheduled 12:00 PM to 1:00 PM. Dinner clusters between 5:30 PM and 7:30 PM, earlier than in many European countries. Summer daylight pushes dinner slightly later and moves it outdoors.
Calling across zones
Calling from one US time zone to another means knowing the offset. A 9:00 AM call from New York hits Los Angeles at 6:00 AM, which is too early. A 5:00 PM call from Los Angeles lands in New York at 8:00 PM, which is usually acceptable. The three-hour maximum difference between Eastern and Pacific Time is manageable but easy to forget.
Canada shares the same zones and nearly the same DST schedule. Most of Saskatchewan stays on Central Standard Time year-round. Small parts of British Columbia, Ontario, and Quebec also skip DST. Mexico abolished DST nationally in October 2022, except for the Baja California border region, which follows the US DST schedule for economic alignment. Check current Mexican rules before scheduling.
Europe runs 5 to 8 hours ahead of US zones, depending on the US zone and the time of year. European DST starts on the last Sunday in March and ends on the last Sunday in October, creating brief windows where the offset differs from the usual gap.
Broadcasting and live events
Network prime time runs 8:00 PM to 11:00 PM Eastern and Pacific. Central and Mountain zones get separate feeds. Live events like the Super Bowl and the Oscars typically start around 6:30 PM ET so West Coast viewers can watch at 3:30 PM PT. Morning news programs air 7:00 AM to 9:00 AM ET; the West Coast gets a tape delay or a 4:00 AM PT live feed.
Sports scheduling is a compromise. East Coast games start late for West Coast viewers. West Coast games end very late for East Coast viewers. Monday Night Football typically kicks off around 8:15 PM ET.
Professions where time zones are critical
Technology and transportation
Software developers must handle time zone conversions, UTC storage, and DST transitions in code. IANA tzdata updates are essential. Airline and transportation workers schedule across zones and work through DST transition nights.
Media and finance
Broadcasters feed network programming on Eastern Time and announce live events with "8/7 Central" notation. Financial traders track market opens and closes across global exchanges. Remote managers schedule meetings across multiple US zones.
Health and safety
Healthcare workers manage shift changes, medication timing, and the documented spike in car accidents, workplace injuries, and heart attacks in the two to three days after the spring-forward switch. The fall-back switch sees a temporary decrease in accidents. The military uses UTC (Zulu time) and the 24-hour clock for all operations.