Sleep Calculator
Choose when you want to wake up (or when you are going to bed), and get times that line up with complete sleep cycles.
How sleep cycles work
Sleep runs in cycles of about 90 minutes: light sleep, deep sleep, then dream (REM) sleep. Waking up at the end of a cycle usually feels easier than being woken from deep sleep in the middle of one. The calculator counts back (or forward) in 90-minute steps and adds the time it takes you to fall asleep.
How much sleep do you need?
- Most adults need 7–9 hours, which is 5 or 6 cycles.
- Teenagers usually need 8–10 hours, and children more.
- Cycle length differs between people (roughly 80–110 minutes), so treat the times as a guide and adjust by 15 minutes if you still wake up tired.
For better sleep, keep the same wake-up time every day, including weekends, and avoid screens and caffeine late in the evening. This tool gives general guidance and is not medical advice. If you snore loudly, stop breathing at night or feel very sleepy in the day, speak to a doctor.
How it works
- Enter — type or paste your values or text.
- Get the result — it is worked out in your browser.
- Adjust — change the inputs to compare, or copy the result.
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