Sleep Cycle Bedtime Calculator
Enter your wake-up time and how many sleep cycles you want to complete to find a bedtime that aligns with natural 90-minute sleep cycles.
Sleep Cycle Bedtime Calculator
Works backward from your wake-up time to suggest a bedtime aligned with complete 90-minute sleep cycles.
This calculator works backward from your target wake-up time, subtracting whole 90-minute sleep cycles (5 cycles ≈ 7.5 hours, 6 cycles ≈ 9 hours) plus your typical time to fall asleep, to suggest a bedtime that lines up with a complete cycle rather than leaving you waking mid-cycle. The result correctly wraps around midnight and is shown on a 24-hour clock, so a suggested bedtime the evening before your wake-up time is handled automatically without confusing negative values.
Example
- With the default values shown above, this calculator returns: Total Sleep Time ≈ 7.5 hours; Raw Bedtime (unwrapped) ≈ -0.75; Suggested Bedtime (24h clock) ≈ 23.25 (24h).
Frequently Asked Questions
Why 90-minute cycles?
Sleep researchers commonly describe a full sleep cycle (moving through light, deep and REM sleep) as lasting roughly 90 minutes, so timing your sleep in whole cycles is associated with waking up feeling less groggy than waking mid-cycle.
How do I read the suggested bedtime?
The bedtime is shown on a 24-hour clock (e.g. 23.25 means about 11:15 PM) — it already wraps correctly even if the calculated bedtime falls on the previous day.
Why include time to fall asleep?
Sleep cycles start once you're actually asleep, not when you get into bed, so this adds your typical time to fall asleep on top of the cycle-based sleep duration.
Sources
- Standard formula, publicly documented method