Sleep Calculator
Calculates bedtimes that let you wake up refreshed on 90-minute sleep cycles around your wake time.
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Enter the time you need to wake up and it suggests bedtimes that land at the end of a 90-minute sleep cycle so you wake up refreshed. It also works in reverse, telling you what time to wake if you fall asleep now, to help cut morning grogginess.
How to use
- Choose the 'Wake time to Bedtime' or 'Bedtime to Wake time' tab.
- Enter your reference time (e.g., 7:00 AM).
- Pick one of the 5-6 cycle options (marked with a green recommendation) from the suggested-time list.
- Save a suggested time with 'Copy result' and use it for your alarm.
FAQ
- Why is the sleep cycle 90 minutes?
- Light sleep, deep sleep, and REM sleep take an average of about 90 minutes to complete one cycle. Waking during the light-sleep phase at the end of a cycle feels far more refreshing, even with the same amount of sleep.
- How many cycles should I sleep?
- Adults are generally recommended 5-6 cycles (about 7.5-9 hours). Prioritize the times marked with a green 'recommended' label in the calculator.
- Can I trust the results as-is?
- Sleep cycles vary from 80 to 110 minutes per person and the time it takes to fall asleep differs widely too, so treat this as a reference. Use it over a few days to find the cycle that works for you.