Twice a year, most of North America and Europe move their clocks by an hour — but not on the same weekends, and not without consequences. The spring change, when clocks jump forward and an hour of the night disappears, is the one researchers watch: sleep shortens, Monday mornings feel heavier, and scientists have spent decades arguing about whether accidents and heart problems briefly rise. This article sets out when the change happens in the US, UK and Europe, what the evidence actually shows, and how to shift your sleep over three or four days instead of one rough night.
The dates differ across the Atlantic
In the United States and Canada, daylight saving time begins on the second Sunday in March and ends on the first Sunday in November. In the United Kingdom and the European Union, summer time begins on the last Sunday in March and ends on the last Sunday in October. That leaves a two-to-three-week gap each spring, and about a week each autumn, when the usual time differences shrink by an hour — New York to London is four hours instead of five. Travellers crossing the Atlantic in those gap weeks occasionally land an hour out in their own plans. The EU has debated abolishing the change since 2018, but member states have not agreed, so the twice-yearly switch continues on both continents for now.
What the spring change does to sleep
The autumn change gives an hour back; the spring change takes one away, and sleep pays. Analyses of sleep diaries, surveys and wearable data generally find that people sleep roughly 30–40 minutes less on the night of the spring transition, with smaller knock-on losses and more fragmented sleep for several nights afterwards as body clocks adjust to the new light pattern. Laboratory studies of circadian timing suggest the body clock can shift by roughly an hour a day at best, which is why a change that looks trivial on the clock face is not trivial to the brain. The effect is not evenly spread: teenagers, evening types (‘night owls’) and people already sleeping too little tend to struggle most, while the autumn transition mainly shifts sleep timing rather than cutting it. For most healthy adults the disruption is real but modest, and gone within a week.
Accidents and heart health: signals, honestly uncertain
Headlines often claim the clock change kills. The careful reading is narrower. A well-known US analysis found fatal traffic accidents rose by about 6% in the week after the spring change, and Swedish registry research found a small rise in heart attacks in the first days after spring forward (and a slight fall after autumn back). Other studies, in other countries and years, found smaller effects or none at all, and all of this research is observational — it cannot fully separate the lost hour from darker mornings, weather or changed routines. The fair summary: there is probably a small, short-lived increase in risk for a few days each spring, far smaller than the risks from chronic sleep loss, and no comparable harm is established for the autumn change. A reasonable response is awareness, not alarm.
How to adjust over three to four days
Treat the change like a one-hour trip across time zones and start early. For three nights before the spring change, go to bed and get up 15–20 minutes earlier each day, so the jump on Sunday feels small. Get outside into morning light soon after waking — light is the strongest signal for resetting your body clock — and keep your wake time fixed even on the weekend. In the evening, dim lights in the last hour, keep caffeine to the morning, and avoid using alcohol to force sleepiness; it fragments the second half of the night. If Monday still feels heavy, a short nap of 20–30 minutes before mid-afternoon can help without stealing from the next night. Drivers who feel drowsy on the Monday commute should treat it like driving tired on any other day: share the drive, take a break, or delay the trip.
