Sleep Cycle Calculator
Best times to go to bed
Based on 90-minute sleep cycles and about 15 minutes to fall asleep.
What is Sleep Cycle Calculator
This sleep calculator finds bedtimes and wake-up times that line up with your 90-minute sleep cycles. Waking at the end of a cycle, rather than mid-cycle, is what makes you feel rested instead of groggy. Pick a wake-up time to see when to go to bed, or set a bedtime to see when to wake up.
How to use
- Choose whether you want to set a wake-up time or a bedtime.
- Enter the time, or tap Now to use the current time.
- Read the suggested times, each labelled with cycles and total sleep.
- Aim for one of the recommended options (7.5 or 9 hours).
- Switch between 12h and 24h clock formats if you prefer.
When to use it
Have to be up at 7:00 for work? The calculator shows you should be asleep by 21:45 for six full cycles or 23:15 for five, so you wake between cycles feeling clear-headed. Handy for planning an early start, catching a red-eye flight, or working out a bedtime that still fits a solid night's rest.
Frequently asked questions
How long is one sleep cycle?
About 90 minutes on average. Each cycle moves through light sleep, deep sleep, and REM. Waking at the end of a cycle, rather than in the middle of deep sleep, is what leaves you feeling refreshed.
Why does the calculator add 15 minutes?
Most people take around 15 minutes to actually fall asleep after getting into bed, so the calculator adds that buffer. The suggested times are when to be in bed, not the exact moment you drop off.
How many hours of sleep do I need?
Most adults do best with 7 to 9 hours, which is five to six full cycles. The calculator marks those options as recommended, but children and teenagers usually need more.
Is 6 hours of sleep enough?
Six hours is four cycles. It can work for the occasional short night, but consistently sleeping that little is linked to worse focus and mood. Treat the four-cycle option as a fallback, not a target.
Can I share this tool with my inputs pre-filled?
Yes. The URL updates automatically as you change the time or mode. Copy it from the address bar or use the Share button, and anyone who opens the link will see your exact settings ready to go.
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