How it works
The calculator counts backwards from your wake-up time (or forwards from your bedtime) in blocks of 90 minutes, and adds the time you need to fall asleep. It shows 6, 5, 4 and 3 cycles. Five or six cycles are marked as the ones most adults aim for.
Tips for better sleep
- Keep the same wake-up time every day, even on weekends.
- Avoid caffeine after the afternoon and screens right before bed.
- Drink enough water through the day, using the water intake calculator.
- Travelling? Check the time difference with the time zone converter.
This is general information, not medical advice.
Frequently asked questions
What is a sleep cycle?
A night's sleep is made of repeating cycles of about 90 minutes that move through light sleep, deep sleep and REM (dream) sleep. The exact length varies between 80 and 110 minutes from person to person and night to night.
Why wake at the end of a cycle?
Being woken in the middle of deep sleep often causes sleep inertia, that heavy groggy feeling. Waking at the end of a cycle, in lighter sleep, usually feels easier. The calculator counts whole 90-minute cycles.
How many cycles do I need?
Most adults feel best with 5 or 6 cycles, which is 7.5 to 9 hours. Teenagers need a little more, and some adults do well on 7 hours. Four cycles (6 hours) is a minimum that is better only occasionally.
Why add 15 minutes?
It usually takes about 10–20 minutes to fall asleep. The tool adds your fall-asleep time before the first cycle starts. You can change it if you fall asleep faster or slower.
Is this medical advice?
No. It is a general guide. If you struggle with sleep, snore heavily or feel tired all day, speak to a doctor.