Sleep Calculator
Find the best time to go to bed or wake up based on 90-minute sleep cycles, so you wake up between cycles feeling more rested.
Assumes ~15 minutes to fall asleep · each cycle ≈ 90 minutes
Best bedtime (6 cycles)
9:45 PM (previous day)
6 cycles · 9 hours of sleep
Suggested bedtimes
6 cycles
9 hrs sleep
5 cycles
7.5 hrs sleep
4 cycles
6 hrs sleep
3 cycles
4.5 hrs sleep
Tip: Waking between cycles — when sleep is naturally lightest — tends to feel much easier than being pulled out mid-cycle. If an alarm sounds during deep sleep, even a full 8 hours can leave you groggy.
Frequently Asked Questions
How do sleep cycles work?
A sleep cycle lasts roughly 90 minutes and moves through light sleep, deep sleep, and REM stages. Waking up between cycles — when sleep is naturally lightest — feels far easier than being jolted awake mid-cycle. Planning your bedtime or alarm around complete cycles helps you feel more rested even if total sleep time is similar.
What time should I go to bed to wake up at 7?
To wake at 7:00 AM feeling refreshed, aim for a bedtime that lets you complete 5 or 6 full cycles. Allowing 15 minutes to fall asleep: 6 cycles (9 hrs sleep) → bedtime 9:45 PM; 5 cycles (7.5 hrs sleep) → bedtime 11:15 PM; 4 cycles (6 hrs sleep) → bedtime 12:45 AM. Most adults do best with 5–6 cycles (7.5–9 hours).
How many hours of sleep do I need?
Most adults need 7–9 hours per night, which corresponds to 5–6 complete 90-minute cycles. Teenagers typically need 8–10 hours (5–6+ cycles) and younger children need even more. Consistently getting fewer than 5 cycles (7.5 hours) is associated with impaired cognition, mood, and long-term health.