About sleep cycles
This sleep calculator suggests the best times to go to bed or wake up based on 90-minute sleep cycles. Waking at the end of a cycle, rather than in the middle of deep sleep, helps you feel more refreshed. Tell it when you want to wake up (or when you are going to bed) and it lists the ideal times, allowing about 15 minutes to fall asleep.
How Sleep works
How to use it
- Choose whether you are setting a wake-up time or a bedtime.
- Pick the time.
- The tool lists ideal times for 4–6 full sleep cycles.
Why 90-minute cycles
Sleep moves through cycles of roughly 90 minutes (light, deep and REM sleep). Waking between cycles feels easier than waking mid-cycle, even after the same total time. Most adults do best on 5–6 cycles (7.5–9 hours).
The 15-minute buffer
The calculator adds about 15 minutes for the time it usually takes to fall asleep, so the suggested times reflect real rest, not just time in bed.
Common uses
- Find the best time to wake up
- Work out when to go to bed
- Wake up between sleep cycles
- Plan a nap or early start
- Avoid groggy mid-cycle wake-ups
- Schedule a consistent sleep routine
- Plan sleep around an early appointment
- Improve how rested you feel
Frequently asked questions
How does the sleep calculator work?
It counts back or forward in 90-minute cycles (plus time to fall asleep) to suggest ideal bed or wake times.
How many hours of sleep do I need?
Most adults do best with 7.5–9 hours, which is 5–6 cycles.
Why 90 minutes?
A full sleep cycle averages about 90 minutes; waking at the end feels more refreshing.
Does it account for falling asleep?
Yes — it adds about 15 minutes.
Is this medical advice?
No — it is a helpful guide; see a professional for sleep problems.
Can I use it for naps?
Yes — a single cycle (~90 minutes) makes a good longer nap.
Is anything uploaded?
No — it runs entirely in your browser.
Is it free?
Yes — completely free with no sign-up.