Sleep Calculator
A sleep calculator helps you find the best time to wake up or go to bed based on 90-minute sleep cycles. Your body naturally cycles through light sleep, deep sleep, and REM sleep in roughly 90-minute stages. Waking up at the end of a cycle (during light sleep) feels dramatically better than waking in the middle of deep sleep, even if the total time slept is the same.
Enter when you want to wake up (or when you plan to fall asleep), and we'll show you the best times based on 4, 5, or 6 complete sleep cycles. The National Sleep Foundation recommends 7-9 hours (5-6 cycles) for adults. Includes 15 minutes for falling asleep.
🌙 Best bedtimes
To wake up at — feeling refreshed, head to bed at one of these times:
📌 5 Tips for Better Sleep
- ✓ Stick to 90-min cycles: A full sleep cycle is ~90 minutes. Waking mid-cycle leaves you groggy.
- ✓ Give yourself buffer time: Plan 15 min to fall asleep. Going to bed earlier won't help if you can't drift off.
- ✓ 5–6 cycles is the sweet spot: 7.5 hours (5 cycles) is usually more refreshing than 8 hours (5.3 cycles).
- ✓ Avoid screens 1 hour before bed: Blue light suppresses melatonin, the sleep hormone.
- ✓ Keep a consistent schedule: Going to bed and waking at the same time daily beats weekend catch-up sleep.
Frequently Asked Questions
What is a 90-minute sleep cycle?
A sleep cycle is one full pass through all sleep stages: light sleep (N1), light sleep (N2), deep sleep (N3), and REM sleep. The average cycle is 90 minutes in adults. Most people need 5-6 cycles per night.
How many hours of sleep do I need?
The National Sleep Foundation recommends 7-9 hours for adults (26-64), 8-10 hours for teens (14-17), 9-11 hours for school-age children (6-13), and 10-13 hours for preschoolers (3-5). Older adults (65+) need 7-8 hours.
Is it better to sleep more or wake at the right cycle?
Both matter, but cycle alignment is more impactful per hour. 6 hours of cycle-aligned sleep often feels better than 8 hours of interrupted sleep. The goal is enough cycles AND the right wake time.
Does the 90-minute cycle really work?
Sleep cycle research is real and well-established. The 90-minute average holds for most adults, but individual cycles can range from 70-120 minutes. Use this calculator as a starting point; track your own wake-up energy over 2-3 weeks to find your personal cycle length.
Should I take naps?
Yes — 20-minute 'power naps' are ideal (one full stage of sleep), 90-minute naps complete a full cycle and avoid grogginess. Avoid napping after 3pm if you have trouble sleeping at night.
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Disclaimer: This calculator provides general estimates based on average 90-minute sleep cycles. Individual sleep needs vary. Not medical advice — consult a healthcare provider for chronic sleep issues.