What Is Daylight Saving Time?
Daylight Saving Time (DST) is the practice of advancing clocks by one hour during the warmer months so that evenings have more daylight and mornings have less. In the spring, clocks 'spring forward' by one hour; in the autumn, they 'fall back.' The idea is to make better use of natural daylight during the times of day when most people are active.
DST typically begins in late March or early April in the Northern Hemisphere and in late September or October in the Southern Hemisphere. The exact dates vary by country. The United States, for example, starts DST on the second Sunday of March, while most of Europe begins on the last Sunday of March.
While the concept sounds simple, DST creates an extraordinary amount of complexity for scheduling, technology, and human health. For one hour each spring, clocks skip from 1:59 AM directly to 3:00 AM, meaning 2:00–2:59 AM simply does not exist. In autumn, the hour from 1:00 AM to 1:59 AM occurs twice. These anomalies have caused everything from missed flights to software bugs to disputed legal rulings about the time of birth.
Which Countries Observe DST?
Approximately 70 countries currently observe daylight saving time, but they are concentrated in Europe and North America. Most of Africa, Asia, and South America do not use DST. The reasoning varies: countries near the equator see little variation in daylight hours throughout the year, so the shift provides no benefit. Others, like Russia and China, have abolished DST after deciding the disruption outweighs the advantages.
Notable exceptions and recent changes include: Turkey permanently adopted summer time (UTC+3) in 2016, effectively staying on DST year-round. Argentina, Brazil (most states), and Egypt have all experimented with DST and then abandoned it. Japan has not observed DST since 1951. Australia is split—New South Wales and Victoria observe DST, while Queensland and Western Australia do not.
The European Union voted in 2019 to end mandatory DST, allowing each member state to choose permanent standard or permanent summer time. However, the implementation has been repeatedly delayed as countries struggle to coordinate their choices. The fear is a patchwork of different times across the EU's single market, complicating travel and commerce.
The Energy Argument: Does DST Actually Save Anything?
The original justification for DST was energy conservation. During both World Wars, governments believed that shifting an hour of daylight from morning to evening would reduce the need for artificial lighting and save fuel. For much of the 20th century, this argument went largely unquestioned.
Modern research paints a more nuanced picture. A landmark 2008 study of Indiana (which adopted statewide DST only in 2006, providing a natural before-and-after experiment) found that DST actually increased residential electricity use by about 1%, because the reduction in lighting was more than offset by increased air conditioning use in the longer, hotter evenings.
Other studies have found small savings in some regions and small increases in others, with the net effect hovering around zero. The consensus among energy economists is that whatever savings DST once provided have been eroded by changes in technology (LED lighting uses a fraction of the energy of incandescent bulbs) and lifestyle (people now use electronic devices that consume power regardless of daylight).
Health Effects of Clock Changes
The twice-yearly clock change has measurable effects on human health. In the spring transition, when people lose an hour of sleep, studies have documented a 24% increase in heart attacks on the Monday following the change. There are also spikes in traffic accidents, workplace injuries, and emergency room visits for mood disorders in the days after clocks spring forward.
The autumn transition, when people gain an hour, is less harmful but still disruptive. Sleep researchers note that it takes most people about a week to fully adjust to either change. For people with sleep disorders, depression, or other health conditions, the adjustment period can be significantly longer.
These health effects have become one of the strongest arguments for abolishing the biannual clock change. Medical organizations including the American Academy of Sleep Medicine have formally recommended ending DST transitions, though they favor permanent standard time (which aligns better with the body's circadian rhythm) over permanent summer time.
DST and International Scheduling Nightmares
For anyone who schedules meetings across borders, DST is a recurring headache. The problem is not just that clocks change—it is that they change on different dates in different countries. The US springs forward in mid-March, Europe waits until late March, and the Southern Hemisphere falls back in March or April. During those transition windows, the time difference between two cities can shift by one or even two hours compared to the rest of the year.
Consider a team with members in New York and London. For most of the year, London is five hours ahead. But for three weeks in March, after the US has sprung forward but before the UK does, the gap narrows to four hours. A standing 3 PM New York / 8 PM London meeting suddenly becomes 3 PM New York / 7 PM London—which might be fine, or might conflict with someone's evening plans.
The safest approach is to use timezone-aware scheduling tools like TimeMeet that automatically account for DST transitions. Never hard-code time differences between cities; always let the software compute the current offset based on the IANA timezone database, which is updated whenever a government changes its DST rules.
Countries That Abolished DST
A growing number of countries have decided that DST is more trouble than it is worth. Russia is perhaps the most prominent example: after years of complaints about the biannual disruption, President Medvedev moved Russia to permanent summer time in 2011. When citizens complained that winter mornings were too dark, President Putin switched the country to permanent standard time in 2014.
China unified its timekeeping in 1949, abolishing DST and adopting a single time zone (UTC+8) for the entire country. India has never observed DST. South Korea last used DST in 1988 during the Seoul Olympics. Brazil, which had observed DST for decades, abolished it in 2019 after studies showed negligible energy savings.
The trend is clear: countries that re-evaluate DST tend to abandon it. The remaining holdouts are largely in Europe and North America, where the political inertia of existing systems and the complexity of coordinating change across multiple jurisdictions have slowed reform.
How to Protect Your Schedule During DST Transitions
If you manage international meetings, DST transitions deserve a place on your calendar as events in their own right. Two weeks before any major DST change (US, EU, Australia), review all recurring meetings and verify that the times still work for everyone after the shift. TimeMeet's planner makes this easy—just set the date to post-transition and check the overlap windows.
Send a brief reminder to all meeting participants one week before the change: 'Heads up—US clocks spring forward on March 8. Our Monday standup will shift for those outside the US. Here are the new times.' This simple act prevents confusion and no-shows.
For critical systems (deployment schedules, on-call rotations, SLA windows), automate the adjustment. Use timezone-aware cron jobs (never hard-code UTC offsets), and test your scheduling logic with dates that fall during transition periods. A little preparation saves a lot of Monday-morning chaos.