Find the best time to go to sleep for the time you need to wake up, or the best time to set your alarm if you’re going to bed now. It plans around 90-minute sleep cycles, so you wake up between cycles rather than in the middle of deep sleep.
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How sleep cycles work
During the night you move through light sleep, deep sleep and REM (dreaming) sleep in cycles of roughly 90 minutes, repeating four to six times. Waking from deep sleep is what leaves many people feeling groggy, a feeling called sleep inertia. Waking at the end of a cycle tends to feel easier.
The calculator also adds the time it takes you to fall asleep. For most people that’s 10 to 20 minutes.
Worked examples
Waking at 7:00
Allowing 15 minutes to fall asleep, the best bedtimes are 21:45 (6 cycles, 9 hours), 23:15 (5 cycles, 7.5 hours) or 00:45 (4 cycles, 6 hours).
Going to bed at 22:30
Set an alarm for 6:15 (5 cycles) or 7:45 (6 cycles) rather than 7:00, which might fall in the middle of a cycle.
How much sleep do you need?
- Most adults need 7 to 9 hours a night.
- Teenagers need 8 to 10 hours, and younger children more.
- A regular wake-up time every day, including weekends, is one of the most effective ways to sleep better.
Cycle length varies from person to person and through the night, so use these times as a guide. If you regularly struggle to sleep or feel exhausted, speak to a GP.
Frequently asked questions
How long is a sleep cycle?
About 90 minutes on average, though it can range from about 70 to 120 minutes and varies through the night.
Is 6 hours of sleep enough?
For most adults, no. Guidance recommends 7 to 9 hours. Regularly sleeping less is linked with poorer health and concentration.
Why do I wake up tired after 8 hours?
You may be waking in deep sleep, or your sleep may be disrupted by alcohol, caffeine, screens, stress or a condition such as sleep apnoea.
Does this work for naps?
Short naps of 10 to 20 minutes avoid deep sleep. A 90-minute nap covers one full cycle.
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