American Daylight Time
The Sunshine Protection Act The US Congress is working on a law that will officially end daylight savings time by effectively setting the clocks ahead one last time and remaining on the advanced time zones. The actual mechanics of the law is to redefine the standard time zones used by the US to be one hour ahead of the current standard times. (EST becomes four hours behind UTC instead of five. CST becomes five hours behind UTC instead of six. MST becomes six hours behind UTC instead of seven. PST becomes seven hours behind UTC instead of eight. Hawaii and Alaska also get an extra hour. All nine US time zones are affected.) After the adjustments the option to follow daylight saving time is removed except for the states/territories/possessions who are currently not following DST (Arizona, Hawaii, Puerto Rico, Guam and the Northern Mariana Islands). These areas will have the option to remain on their current time zone or spring forward into the newly defined time zones. While "freezing the clock" has become more popular in recent years the decision over which time to remain on comes down to whether people prefer an earlier sunrise or a later sunset. The Sunshine Protection Act was first introduced in 2018 and has been reintroduced in every session of Congress since. The furthest the bill has progressed was in 2021 when it was passed by the senate (Unanimous Consent) but was not debated in the house. In 2026 the bill was passed by the house (308-117) but has not been put up for a senate floor vote. The current attempt at passage will expire at the end of the session in 2026. (More details) If the current proposal is adopted, sunrise will occur after 9am a few days per year in several parts of the country. The earliest sunset will be after 5pm in most of the country. This is the trade off of changing the time zones. Standard Time These two maps are shaded for standard time and show the latest sunrise and earliest sunset experienced each year. Over the course of a year the sun will rise no later and set no sooner than shown on these maps. The dividing lines have been adjusted since time zones were first regulated in 1918 but these extremes have applied every year except 1942-1945 ("War Time" permanent DST) and 1974-1975 ("Emergency DST" extended DST). Time Zone Divisions Move West Time zone divisions are set "for the convenience of commerce" with nearly all adjustments moving lines west, including more areas in eastern time zones. Shown here is the gradual shift west of the division between the central time zone and the eastern time zone. The current division is the gray line through each image. State lines are not shown except as a time zone division. 1913 represents railroad time zones based on drawing straight lines between a few named cities. The federal government defined exact lines in 1918. Most of the 1918 boundaries referenced railroads. The last railroad reference in the eastern time boundary shown was removed in 1960, moved to county lines and geological features. Prior to 1967 observance of DST was regional and random with some areas observing DST on different dates or not at all with no federal law preventing variances. The Uniform Time Act of 1966 regulated Daylight Saving Time nationwide, setting nationwide dates for the beginning and end of DST and allowing states to opt out. Indiana and Michigan expanded eastern time to the west and exempted their states from daylight saving time (affecting the areas in cyan below). Unofficial observance of a neighboring time zone continued in four counties in northern Michigan (until 1973) and five counties in southeast Indiana (until 2005). Michigan began observing DST in 1973 and the four counties near Wisconsin officially moved into central time. Congress corrected the DST opt out law in 1972. Two Indiana counties separately moved to eastern time prior to Indiana passing a law repealing their DST exemption in 2005 (effective 2006). At the request of the state of Indiana the US DOT held hearings to adjust the boundary line. Six of the eight counties moved to central time returned to eastern time. Similar adjustments were made to the divisions between mountain and central time and mountain and Pacific time. The railroad defined zones had El Paso as a meeting place between railroads operating on Pacific time to the west, central time to the east and mountain time to the north. The zones defined by the ICC in 1918 followed generally north-south lines. The ICC made an adjustment in 1919 returning western Montana to mountain time. Congress made an adjustment in 1921 to move western Oklahoma and Texas into Central time. Congress also moved southern Idaho to mountain time in 1923. The division between mountain and Pacific time has not changed since 1969. The 1921 Federal law allowed two Texas counties near El Paso the option of returning to mountain time. (Locally observed times became official in 1970.) Additional counties were added to central time in 1990, 1992, 2003 and 2010 as shown. Note the net moves to the west of time zone division lines from 1918 to current. (Maps do not show DST observance prior to 1967.) Length of Daylight Saving Time Expands The number of weeks DST is followed has increased from 1918 to the current standard introduced in 2007. Each move of the division line to the west provided an additional hour of afternoon / evening sun for the area affected. Each increase in the number of weeks daylight saving time was observed provided an additional hour of afternoon / evening sun during the added weeks. (An added afternoon / evening hour is at the cost of a morning hour of sun.) Permanent DST The map below illustrates the earliest sunset time if the proposed change to "permanent DST" becomes law. Areas in yellow will have their earliest sunset after 6pm. Areas in green will have their earliest sunset between 5pm and 6pm. Areas in blue will have their earliest sunset before 5pm. Later sunsets is the benefit of Permanent DST. Note the areas receiving the largest benefit from the change include the most populated cities in the northern United States. (Permanent DST was observed from 1942 to 1945 as "War Time" as an effort to support the war effort by saving energy.) (DST was extended in 1974 and 1975 as an effort to save energy during an energy crisis. Permanent DST was passed but repealed for Oct 1974-Feb 1975.) (Emergency Daylight Saving Time Energy Conservation Act of 1973) The cost of adjusting clocks for a later sunset is a later sunrise. The map below illustrates the latest sunrise times across the continental US, based on the adoption of "permanent DST". The blue areas will have a latest sunrise after 9am. The green areas will have a latest sunrise between 8am and 9am. The yellow areas will have a latest sunrise before 8am. Northern cities such as Detroit and Indianapolis will have sunrises near or after 9am. All areas with a later than 9am sunrise will also have a later than 5pm sunset with some areas with a sunset after 6pm. Southern states will be less affected by the change. The shortest days of the year across the southern US are ten hours vs the nine hour shortest days seen across the northern US. The length of the shortest day of the year is shown to the right. Note that the maps above show extremes (a few days in late December and early January). Sunrise will be before 9am and sunset after 5pm nationwide most of the year. The move to "permanent DST" is being driven by people who prefer the hour of sun at the end of the day instead of at the beginning of the day. Sunrise and Sunset in Selected Cities A look at 14 cities across the United States Permanent DST and Natural Time A detailed look at sunrise and sunset
The Neighbors Are Locking Their Clocks
Canada and Mexico	Canada moves toward Permanent DST (all provinces from Manitoba to the west have permanent DST) Mexico has moved to Permanent Standard Time
Reference Material
Legislative Details	SUBCHAPTER IX—STANDARD TIME with proposed modifications
ADDITIONAL LEGISLATIVE HISTORY The Calder Act War Time (WW II) Uniform Time Act of 1966 Emergency DST Act Late 20th Century Early 21st Century 1918-1948 1942-1945 1966/1972 1974-1975 1983/1986/2000 2005/2007
Didn't we try this before?	Emergency Daylight Saving Time Energy Conservation Act of 1973 A poorly implemented attempt at permanent DST DST began January 6th, 1974 - adding an hour of morning darkness the day with the latest sunrise of the year Michigan, Indiana and Kentucky opted out, remaining on standard time year-round Traffic accidents in the morning were balanced by less accidents in the evening The energy savings desired were proven, leading to extending DST in 1986 and 2006
Solar Based Time Zone Divisions In 1883 the railroads set coordinated time to avoid issues scheduling trains across the country. Local solar time did not work well with each city and town along the route having a different "noon". In 1918 the Federal government took control of the clocks and delegated control over time zones to the Interstate Commerce Commission (ICC). At the end of the year, the ICC approved their first set of division lines for time zones. The railroad time zones were based on each company's operations leading to a map defined by cities in each zone connected by straight lines. The ICC's first map adjusted the lines to be closer to being meridians. The line through Montana, Idaho, Utah and Arizona followed railroads to divide Pacific from mountain time. The line through Ohio, Kentucky, Virginia, Tennesee, Georgia and Florida followed railroads to divide central time from eastern time. Both of those lines generally following solar meridians. The division line between mountain and central time was created to the west of the solar meridian. These lines divided communities. While the definitions included the limits of each city or town the line passed through it created a situation where municipal limits became the time zone line. If you lived or ran a business outside of the municipal limits you could be in a different time zone than the municipality. Many communities followed the zone of their choice, regardless of the Federal standard. This included communities choosing to follow daylight saving time (or not) on their own schedules. The gray lines on each map are the current time zone boundries, last changed in 2010. The shading represents the time zone assigned based on the railroad's preference (left) and the first attempt to define a line by the ICC in 1918 (right). The vertical red lines represent meridians based on "solar time" with no location more than 30 minutes ahead of or behind "solar noon". As time passed it became clear that the lines needed to be moved to other features than railroads, often to state lines, county lines and other geographic features that were easier to define than municipal limits. Those moves have nearly all been to the west of the previous line, with people prefering their commercial ties to cities in the east part of the country over having solar noon match their clocks. Aproximately 47% of the US population lives in the eastern time zone, providing a convenient common schedule. 29% live in the central time zone, with the third largest city in the US (Chicago) anchoring their time zone. 15% live in the Pacific time zone anchored by the second largest city in the US (Los Angeles). With the current zones, a small portion of Maine is the only area that is east of a solar based time zone limit. Every other division line has been drawn to the west of the meridian. Alaskan Time Zones In 1918 the Calder Act set one time zone for the territory of Alaska using the 150 west meridian as a reference. The Uniform Time Act of 1966 split the state into four time zones, following meridians at 135, 150 and 165. Eastern Alaska (including Juneau) was placed in Pacific time matching the neighboring Canadian province of British Columbia. A portion of the coastline was placed in Yukon Time (UTC-09 served the western edge of Yukon in Canada until 1972). In 1983 the four zones were restructured into two zones, Alaska Standard Time covering most of the state and Hawaii-Aleutian Standard Time covering the Aleutian Islands. This placed most of the state an hour ahead of the initial 1918 single time zone and the Aleutian Islands two hours ahead of ships in international waters offshore. Alaska was purchased from Russia on March 30th, 1867, and incorporated as a territory August 24th, 1912. Alaska achieved statehood January 3rd, 1959. The 1966 zones were defined by meridians: Pacific time east of 137 west; Yukon time between 141 west and 137 west; Alaska-Hawaii time between 162 west and 141 west (including all of Hawaii); and Bering time west of 162 west. The time shown at the bottom of each map reflect the meridian based time used in international waters. The 200nm Exclusive Economical Area around the US and Canadian coasts is also shown. Note that the international date line runs between Alaska and Russia along the western edge of both zones. Yukon and British Columbia in Canada now follow UTC-07 year-round, two hours ahead of the current winter standard time in Alaska. The Sunshine Protection Act will make DST permanent, placing most of Alaska two hours ahead of the original 1918 time and the Aleutians three hours ahead of international waters. The State of Alaska generally supports this change and legislation has been introduced at the state level to make the change by moving the state into the Pacific time zone and ending DST.