When should you sleep?
90-minute cycles. Wake up refreshed.
Medical Disclaimer: This tool provides general educational estimates. Always consult your prescribing physician or healthcare provider before making medication changes or interpreting results from population-based models.
Frequently Asked Questions
Sleep occurs in 90-minute cycles through light sleep, deep sleep, and REM stages. Waking at the end of a complete cycle (rather than mid-cycle) helps you feel refreshed. Most adults need 5-6 complete cycles (7.5-9 hours).
The National Sleep Foundation recommends 7-9 hours for adults (18-64), 7-8 hours for older adults (65+), and 8-10 hours for teens (14-17). Individual needs vary.
To wake at 7 AM after 5 sleep cycles (7.5 hours) plus 15 minutes to fall asleep, go to bed at 11:15 PM. For 6 cycles (9 hours), go to bed at 9:45 PM.
Sources
- Hirshkowitz M, et al. National Sleep Foundation's sleep time duration recommendations. Sleep Health. 2015;1(1):40-43. Link
- Walker M. Why We Sleep: Unlocking the Power of Sleep and Dreams. Scribner; 2017.
Methodology
This calculator uses the standard 90-minute sleep cycle model. Each cycle progresses through light sleep (N1, N2), deep sleep (N3), and REM sleep. Total sleep time = (number of cycles × 90 minutes) + time to fall asleep. Waking between cycles reduces sleep inertia (grogginess).
Sleep occurs in 90-minute cycles. To wake refreshed, time your bedtime so you complete 5-6 full cycles. For a 7 AM wake time with 15 minutes to fall asleep: 5 cycles = 11:15 PM bedtime, 6 cycles = 9:45 PM. Adults need 7-9 hours per the National Sleep Foundation.
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