How to use the Sleep Cycle
- Enter the time you must wake up.
- Read the suggested bedtimes, each one cycle apart.
- Allow the built-in 15 minutes for falling asleep.
- Aim for five or six complete cycles rather than a fixed number of hours.
How the calculation works
A full cycle progresses through light sleep, deep slow-wave sleep and REM, averaging about 90 minutes but ranging from 70 to 120 between individuals and across the night. Deep sleep dominates early cycles and REM lengthens toward morning, which is why cutting the last two hours removes disproportionately more REM than total time suggests. Waking during deep sleep produces sleep inertia — the heavy, disoriented feeling that can persist for half an hour.
Five cycles gives 7.5 hours and six gives 9, bracketing the 7 to 9 hours most adults need. Counting backwards from wake time and adding roughly 15 minutes of sleep latency lands you at a cycle boundary. Consistency matters more than precision: a regular schedule, including at weekends, stabilises circadian rhythm far more effectively than optimising any single night, and cycle length varies enough that the calculation is a guide rather than a guarantee.
Bedtime = wake time − (cycles × 90 minutes) − 15 minutes to fall asleepSource: Sleep architecture and 90-minute ultradian cycle research; adult sleep duration guidance per the National Sleep Foundation.
Worked example
Needing to wake at 06:30.
- Six cycles = 540 minutes; 06:30 − 9:00 = 21:30, less 15 minutes = 21:15.
- Five cycles = 450 minutes; 06:30 − 7:30 = 23:00, less 15 = 22:45.
- Four cycles = 360 minutes; bedtime 00:15.
Best bedtimes are 21:15 or 22:45. For most adults 22:45 is the practical target, giving five full cycles and 7.5 hours.
Frequently asked questions
Is 90 minutes the same for everyone?+
No — cycles range from about 70 to 120 minutes and vary across the night. Treat the calculation as a guide and adjust based on how you actually feel waking up.
Is six hours enough if it is three full cycles?+
Rarely. Most adults need 7 to 9 hours, and consistently sleeping six accumulates a deficit that affects cognition and health regardless of where cycles fall.
Why do I feel worse after a long lie-in?+
Waking mid-cycle causes sleep inertia, and an irregular schedule disrupts your circadian rhythm. Consistent timing usually beats extra weekend hours.
Do naps follow the same rule?+
Short naps of 10 to 20 minutes avoid deep sleep and refresh without grogginess. A full 90-minute nap completes a cycle; anything between the two risks waking in deep sleep.
Last reviewed August 31, 2026. We review this page whenever the underlying formula, tax year, published rate or standard changes.