What the clocks changing does to your sleep (and how to adjust)

By Naresh Singh · 28 October 2026 · 6 min read

Twice a year, many of us move our clocks by an hour and are told it's no big deal. Yet plenty of people find they wake too early, feel groggy in the afternoon or lie awake at bedtime for several days afterwards. One hour sounds small, but it's a sudden change to a schedule your body has spent months settling into. Here's what's going on, and some practical ways to make the switch easier.

1. When the clocks change

The dates depend on where you live:

• UK and EU: clocks go back one hour on the last Sunday of October (in 2026, that's 25 October) and go forward on the last Sunday of March (28 March 2027).
• US and Canada: clocks "fall back" on the first Sunday of November (1 November 2026) and "spring forward" on the second Sunday of March (14 March 2027).

The change happens in the early hours of Sunday morning. Not every place observes daylight saving time; for example, most of Arizona and all of Hawaii in the US don't change their clocks, and many countries outside Europe and North America don't either. Your iPhone updates its clock automatically, but your body doesn't.

2. Why one hour can throw you off

Your body runs on an internal clock, the circadian rhythm, which roughly follows a 24-hour cycle. It helps decide when you feel sleepy, when you feel alert, and when hormones such as melatonin rise in the evening. The strongest signal that keeps this clock on time is light, especially daylight in the morning and darkness in the evening. Meal times, activity and a regular routine help too.

When the clocks change, your social schedule (work, school, alarms) jumps by an hour overnight, but your internal clock shifts gradually, often taking several days. Until the two line up again, you're asking your body to sleep and wake at times that don't quite match its signals.

• When the clocks go back (autumn), you technically gain an hour. But many people find they still wake at their old time, which is now an hour earlier on the clock. Evenings also get dark sooner, so some people feel sleepy earlier than usual.
• When the clocks go forward (spring), you lose an hour. Bedtime arrives while your body still thinks it's an hour earlier, so falling asleep can be harder, and the alarm goes off at what feels like the middle of the night. Many people find this direction the tougher of the two.

Children, pets and anyone with a tight routine tend to keep to the old timing at first, which can affect everyone in the house.

3. Before the change: shift gradually

The simplest trick is to avoid one big jump and make several small ones instead. For three or four days before the change, move your bedtime and wake time by about 15 minutes a day:

• Before the clocks go back: go to bed and get up about 15 minutes later each day.
• Before the clocks go forward: go to bed and get up about 15 minutes earlier each day.

By Sunday, you'll be most of the way there. It also helps to move meal times and your evening wind-down by the same amount, so all of your daily cues shift together. If you have young children, the same gradual approach with their bedtime often makes the week after much calmer.

4. After the change: light, caffeine and a steady wake time

Keep a consistent wake time

Pick a wake time on the new clock and stick to it every day for the following week, weekends included. A regular wake time is one of the most reliable ways to anchor your rhythm. Resist the urge to sleep in to "catch up"; it can make the next night harder.

Get daylight in the morning

Try to get outside, or at least sit by a bright window, within an hour or so of waking. Morning light helps tell your body clock that the day has started, which is especially useful when the clocks go forward. Even a short walk on a cloudy day gives you far more light than typical indoor lighting.

When the clocks go back and you find yourself waking too early, some people find it helps to get daylight later in the afternoon and to keep the bedroom dark in the early morning.

Watch caffeine and evening light

• Caffeine: it can stay in your system for hours. During the week of the change, try to have your last coffee or tea by early afternoon.
• Evening light: bright overhead lights and screens late in the evening can make it harder to feel sleepy. Dim the lights for the last hour before bed and turn down screen brightness, or use Night Shift on your iPhone.
• Naps: if you need one, keep it short (around 20 minutes) and earlier in the afternoon, so it doesn't eat into your night.
• Alcohol: a drink may make you feel drowsy, but it can make sleep later in the night lighter and more broken.

5. Watch your own sleep for a week

Everyone adjusts at a different pace. Some people feel normal by Monday; for others it takes most of a week. Rather than guessing, it helps to keep an eye on a few simple things for the seven nights after the change, and compare them with the week before:

• What time you actually fell asleep, not just when you went to bed
• What time you woke, and whether it was before your alarm
• How long you slept in total
• How rested you felt mid-morning

You can do this with a notebook, or let your phone do it. DreamWave, the iPhone app I build, records when you fell asleep and woke, how long you slept and a nightly sleep score, with just your phone on the nightstand. Its sleep history makes it easy to see whether your times are drifting back to normal. If you forget to start tracking one night, it can estimate the night from your iPhone's motion history. Its Smart Alarm, which rings within a window of up to 30 minutes when you start to stir, can also take some of the edge off those darker mornings.

If your sleep hasn't settled after a couple of weeks, it's probably not the clocks, and it's worth looking at other causes.