LockTheClock

Fix Daylight Saving Time for good!

Research

Research

What is the science behind #LockTheClock?

There are more than a hundred studies below. They answer two different questions, so the page is organized that way.

The first question is what the twice-yearly clock change does to us. That is the largest body of research, and it is the case for ending the switch. That’s why we’re called Lock The Clock.

The second question is which time we should live on once we stop switching. That research is smaller, and it’s what’s making it so hard for us collectively to make a decision and finally lock the clock.

My view hasn’t changed in more than 10 years of working on this issue: Let’s stop changing the clock and let each state decide what time zone to lock into permanently. Geography matters here more than anything, and each state is in a different physical place and it’s not the job of the federal government, any individual scientist or politician or anyone else to make that decision for the people of each state.

Start here

These are perhaps the best overall looks at DST and how the clock-changing hurts us.

  • European Journal of Epidemiology, 2026 — The most comprehensive review of the field. A team at the University of Kent and the University of Cologne assessed 157 studies from 36 countries and graded each one for quality. Spring transitions are linked to more heart attacks and more fatal traffic accidents. Living with Daylight Saving Time rather than Standard Time is associated with lower all-cause mortality. (Free full text)
  • Review of Economics and Statistics, 2021 — Darkness causes more than £500 million a year in road accident costs in Great Britain. Setting Daylight Saving Time year-round would eliminate 8 percent of that. The authors conclude that looking only at the transition week understates the true cost of the current system.
  • Nature Communications, 2022 — Permanent Daylight Saving Time reduces deaths.
  • Current Biology, 2020 — The spring forward change kills roughly 28 people a year in traffic accidents in the United States alone. (Plain-language summary)
  • Current Biology, 2022 — Permanent Daylight Saving Time would prevent 33 deaths, 2,054 injuries and $1.19 billion in costs every year from deer collisions alone.
  • Deutsches Ärzteblatt International, 2024 — Meta-analysis of 12 studies across 10 countries. Heart attack risk rises about 4 percent in the week after the spring clock change.
  • Review of Economics and Statistics, 2015 — Crime falls when evenings are lighter. One of the most cited papers in this literature.

Part One: What the clock change does

This is the research on the twice-yearly switch itself. It is the strongest and deepest part of the literature.

Heart, stroke and circulation

Mortality and overall health

Sleep and the body clock

Mental health

Other medical conditions

Traffic in the days after the change

Work, money and behavior

Judgment, attention and character

Part Two: Which time we should live on

Once we stop switching, we have to pick one. This is the research on that choice. It compares living under Daylight Saving Time against living under Standard Time, rather than looking at the week after a transition. It is a smaller and more contested body of work than Part One, so it is laid out here as two cases.

Before you read either case, read these three.

Three papers argue that this question deserves a more careful conversation than it usually gets.

  • Voters in the eastern part of a time zone prefer permanent Daylight Saving Time. Voters in the west prefer permanent Standard Time. Where you sit inside a zone changes what the clock actually does to your day, which is a strong argument for phasing any change in and giving states room to sort out their boundaries rather than flipping the country overnight.
    Journal of Biological Rhythms
  • Scientists who favor permanent Standard Time should not push it dogmatically, because doing so alienates the public from science generally. If you are planning to use any of the research on this page to argue that one option is definitively better for every state in the U.S., read this one first.
    Clocks & Sleep
  • Broad declarations about clock time, sun time and sleep are probably too simplistic given how complicated the underlying science is.
    LMU Munich

The case for permanent Daylight Saving Time

Lives saved

  • Permanent Daylight Saving Time reduces deaths.
    Nature Communications and the Journal of Population Economics, which studied Indiana’s 2006 adoption of Daylight Saving Time
  • Darkness costs Great Britain more than £500 million a year in road accidents. Year-round Daylight Saving Time would cut 8 percent of that. The authors argue that focusing on the transition alone understates the cost of the current system.
    Review of Economics and Statistics
  • Across 157 studies from 36 countries, living with Daylight Saving Time rather than Standard Time is associated with lower all-cause mortality.
    European Journal of Epidemiology

Road safety

Crime

Children and schools

Activity, recreation and daily life

Energy and environment

Overall

The case for permanent Standard Time

The argument for Standard Time rests almost entirely on one thing: morning light and its effect on sleep and circadian rhythm. It is a narrower case than the one above, but it is a serious one and it is made by serious researchers.

Sleep and circadian rhythm

Seasonal Affective Disorder

One piece of background worth knowing

This is not a partisan issue, and the widespread belief that farmers wanted Daylight Saving Time has it exactly backwards. Social Science Quarterly

Part Three: Official reports

Government bodies that have studied this and published findings.

  • Congressional Research Service. The standard federal briefing document on Daylight Saving Time, most recently updated in July 2026. Report R45208
  • Massachusetts. The most thorough state-level study anyone has done. Report of the Special Commission on the Commonwealth’s Time Zone (listing page)
  • Washington State, 2019. Found that clock changing is deadly, but did not find strong evidence favoring one permanent time over the other. Worth noting how much research has come out since. Health impact review
  • Missouri, 2022. A clear, short briefing prepared for the state legislature. Summary and full PDF
  • Maine. Public opinion research showing strong support for locking the clock, with 75 percent preferring permanent Daylight Saving Time. Study
  • US Department of Energy, 2008. The congressionally mandated report on the 2007 extension of Daylight Saving Time. Report to Congress

If you would like to use this research, you are of course welcome to, but I would appreciate a link back to this site. Thanks.