Sleep Calculator
Find the best bedtime or wake-up time based on 90-minute sleep cycles
Instructions
Sleep Time Calculator Instructions\n\n## What It Does\nDuring sleep you cycle between light and deep sleep, and one cycle lasts about 90 minutes. Waking at the end of a cycle (during light sleep) usually feels fresher, while being woken during deep sleep tends to leave you groggy. This tool helps you line up your schedule with the end of a cycle.\n\n## How to Use\n1. First choose "How long to fall asleep": the time from lying down to actually sleeping, usually 15 minutes\n2. Mode one, "Sleep now, wake at": count 4-6 cycles forward from the current time\n3. Mode two, "Wake at, sleep at": enter the time you want to get up and count back to the times you should go to bed\n4. Under each time you will see how many full cycles it gives you and the total hours\n\n## Notes\n- 90 minutes is a common estimate and varies a lot between people, so trust how you actually feel\n- Going to bed within 15 minutes either side of a suggested time is fine\n- This is a scheduling tool and does not constitute medical advice; if you often struggle to fall asleep or feel extremely sleepy during the day, see a doctor promptly
FAQ
Why are 4 to 6 cycles recommended?
4 cycles is about 6 hours and 6 cycles is about 9 hours, covering the 6-9 hour range most adults need, so you can pick based on how you actually feel.
Does the "How long to fall asleep" field matter?
Very much. It determines when you actually fall asleep, which in turn affects what time the end of a cycle falls on. If you often lie awake for a long time, choose 25 minutes.
Can I use the result as health advice?
No. It is only a schedule conversion based on a common cycle, not aimed at any illness or condition, and it cannot replace the judgment of a doctor or sleep specialist.
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