How to Adjust to Daylight Saving Time (Spring Forward and Fall Back)

Why one hour is not a trivial hour

One hour sounds like nothing. It is not. Spring forward is a forced one-hour phase advance imposed on an entire population on the same night — the biological equivalent of flying east one time zone, except no one chose to travel and no one changed their light environment to match. Your alarm now goes off when your body clock still reads the old time. The clock on the wall moved; the clock in your brain did not.

The direction is what makes it hard. A phase advance means going to sleep and waking earlier than your body currently wants to. Your internal pacemaker does not want to advance. Left alone in constant conditions, the human circadian clock free-runs with an intrinsic period averaging about 24.18 hours — slightly longer than the solar day (Czeisler et al., 1999). That built-in bias means your body finds it easy to drift later and hard to move earlier. Spring forward asks for exactly the move your physiology resists.

This is the same reason eastward jet lag wrecks people while westward travel is forgivable. Delaying your clock works with the grain of a >24-hour period. Advancing it works against the grain. Fall back, which delays your clock by an hour, is the easy direction — and people still manage to ruin it, which we cover below.

What actually happens to the population after spring forward

The effects are not just grogginess. They show up in hard registry data, at the scale of whole countries, in the days immediately after the spring transition.

Heart attacks rise. A Swedish study covering more than two decades of national data found the incidence of myocardial infarction increased by roughly 5% in the first week after the spring shift to daylight saving time, with the effect concentrated in the first three workdays (Janszky & Ljung, 2008). The same study found the opposite in autumn: shifting back and gaining an hour was followed by a small reduction in heart attacks. Sleep loss and abrupt circadian misalignment are the suspected mechanism.

Fatal car crashes rise too. An analysis of over 730,000 fatal US motor vehicle accidents from 1996–2017 found a 6% spike in fatal crashes during the workweek following spring forward, corresponding to about 28 extra deaths per year (Fritz et al., 2020). Notably, the risk was higher the farther west you live within your time zone — where the clock is already set earlier than the sun, compounding the morning darkness. These are real, documented population effects, but keep the size in perspective: your individual weekly risk change is small. The point is that a one-hour clock shift is biologically real enough to move a national accident and cardiac curve at all.

The fix: absorb the shift before it happens

The single highest-leverage move is to stop treating spring forward as a Sunday event and start treating it as a four-day project that ends on Sunday. If you arrive at the transition already shifted, there is almost nothing left to adjust to.

Beginning the Wednesday or Thursday before, move both your bedtime and your wake time 15–20 minutes earlier each day. By Saturday night you will be within about 15 minutes of the new schedule, and Sunday morning arrives as a formality instead of a shock. Shifting gradually also keeps your sleep pressure and clock roughly aligned, so you actually fall asleep at the earlier bedtime rather than lying awake.

Light is the lever that makes an advance stick. Your circadian clock is most sensitive to light timing relative to your body's biological night: light in the late night and early morning advances your clock earlier, while evening light delays it (Khalsa et al., 2003). To pull your clock earlier, chase morning light and blunt evening light.

• Morning, each day of the shift: Get 15–30 minutes of bright light — ideally outdoors — within an hour of waking. This is the strongest signal telling your clock to move earlier. On the Sunday of spring forward, treat this as non-negotiable.
• Evening, each day of the shift: Dim your environment for 1–2 hours before your new, earlier bedtime. Bright evening light pushes your clock in the wrong direction and directly cancels your morning gains.
• Caffeine: Cut off caffeine by early afternoon (roughly 6–8 hours before your new bedtime). Caffeine has a half-life of 5–7 hours; an afternoon coffee is still active in your system when you are trying to fall asleep an hour earlier than usual.

Protect the Monday

The Monday after spring forward is when the documented risks cluster: it is the first workday, the sleep debt is fresh, and people compound it by staying up Sunday night at their old bedtime. Treat that Monday defensively.

Get outside for morning light before or during your commute. Front-load your hardest thinking into the late morning, when your cortisol awakening response and circadian alerting signal are working in your favor, and be skeptical of your own judgment in the mid-afternoon dip. If you drive, give yourself extra margin — this is precisely the window the crash data points to. Do not try to 'catch up' with a large afternoon nap, which will bleed off sleep pressure and make the earlier bedtime impossible again.

If you did no preparation and Sunday has already arrived, you can still salvage it: get aggressive morning light, hold a firm earlier bedtime, protect caffeine timing, and expect to feel roughly adjusted within 3–5 days rather than the same night. A tool like Soja can generate the day-by-day light, caffeine, and sleep-window schedule if you would rather not build the plan yourself.

Fall back: the easy direction people still ruin

Fall back delays your clock by an hour, which is the direction your >24-hour physiology already favors. It should be nearly free. Most people sabotage it in one predictable way: they treat the extra hour as a bonus and sleep in.

The instinct is to enjoy the 'extra hour' by staying in bed later on Sunday morning. That instinct is wrong. Sleeping in pushes your clock even later and turns a one-hour delay into a self-inflicted case of social jet lag that lingers for days, especially with the earlier winter sunsets pulling you later anyway.

Instead, hold your normal wake time. Get up at your usual clock time on the Sunday of fall back, get morning light, and go to bed at your normal clock time that night. You will feel slightly sleepy earlier in the evening for a day or two — that is your clock settling into the new time correctly. Anchoring your wake time is the whole trick.