How does the clock change planner work?
- Choose where you live. The US and Canada and the UK and Europe change on different dates, and the planner shows the next one for each. Elsewhere, it shows the plan without dates.
- Choose the change. Spring forward, when clocks go ahead an hour, or fall back, when they go back an hour. The next change is picked for you.
- Enter your usual bedtime and wake time.
- Pick how many nights and how big a step. Two to four nights, moving 15 or 20 minutes a night.
- Follow the nights in order. Each night shows your bedtime and the next morning's wake time, then what to do on the night of the change and the days after.
Nothing you enter is stored.
Why does a one-hour clock change affect sleep?
Your body clock does not move when the clocks do. On the morning after clocks spring forward, a 7am alarm goes off at what your body still treats as 6am. After they fall back, you tend to wake an hour early.
An American Academy of Sleep Medicine advisory found lower total sleep time and sleep quality after the change, and in some studies lower scores on daytime tests of thinking. It says the "effects on sleep/wake patterns can last approximately five to seven days", and advises people whose work needs full alertness to "exercise particular caution for at least seven days" after the change. The effects are strongest in people who are already short on sleep.
How do you prepare for clocks springing forward?
Move your sleep earlier in small steps. The academy's daylight saving time advice is to start "two to three nights before the time change" and "Shift your bedtime 15 or 20 minutes earlier each night."
- Shift your wake time too, by the same amount, so the shorter evening is not just lost sleep.
- Move dinner earlier. The academy suggests other daily time cues follow, for example "start eating dinner a little earlier each night."
- On the night of the change, set your clocks ahead in the early evening and go to bed at your usual time on the new clock.
- The next morning, "Head outdoors for some early morning sunlight", which the academy says "will help set your internal clock."
Three nights of 20 minutes covers the whole hour before the change. Steps of 15 minutes cover most of it, and the rest catches up in the first few days after.
How do you prepare for clocks falling back?
Do the same in the other direction. The academy's Sleep Education guide suggests going to bed 15 to 20 minutes later each night for a few nights before the fall change.
There is one exception. If you have been short on sleep for a while, the same guide says to skip the later bedtimes: "you will benefit from getting an 'extra' hour of sleep on the night when you 'fall back' to standard time." Tick the box in the planner and it gives you that version.
Why does light help after a clock change?
Daylight is the main signal your body clock follows, and its effect depends on timing. A 2019 review in Frontiers in Physiology explains that light in the hours after the clock's daily low point, roughly the early morning, moves the clock earlier, while light in the hours before it, the evening and night, moves it later.
| Change | Your clock needs to move | Light that helps |
|---|---|---|
| Spring forward | One hour earlier | Morning daylight |
| Fall back | One hour later | Afternoon and evening daylight |
For bigger shifts, such as flying across several time zones, the same idea scales up in our jet lag planner.
When do the clocks change?
- US and Canada: clocks go ahead on the second Sunday in March and back on the first Sunday in November, at 2am local time. A few places, such as most of Arizona and Hawaii, do not change.
- UK and Europe: clocks go ahead on the last Sunday in March and back on the last Sunday in October.
- Elsewhere: many countries do not change their clocks at all, and those that do often use other dates. The planner still works without dates.
Who should take the clock change most seriously?
Anyone who is already short on sleep, because the academy found the effects "most notable when people are not getting healthy amounts of sleep at the time of the clock change." Aim for at least 7 hours a night before and after the change. If you feel drowsy in the days after, take extra care driving or using machinery.
The steady habits in the sleep hygiene checklist make any change easier to absorb, and the social jetlag calculator shows whether your weekends already shift your clock by more than an hour. The full guide to sleep covers the rest.
