Sleep Calculator
Find the best bedtime or wake-up time based on sleep cycles.
Best bedtimes
9:15 PM or 10:45 PM
6 cycles (9 h)
9:15 PM
5 cycles (7.5 h)
10:45 PM
4 cycles (6 h)
12:15 AM
Assumes ~15 minutes to fall asleep and 90-minute sleep cycles.
Waking between cycles
Sleep runs in ~90-minute cycles from light to deep to REM. Waking at a cycle boundary — after 7.5 or 9 hours rather than 8 — often feels better than waking mid-deep-sleep, which is the groggy 'sleep inertia' feeling an alarm mid-cycle produces.
Consistency beats optimization
Adults need 7–9 hours; teens more. A steady schedule — same bedtime and wake time, weekends included — does more for sleep quality than any calculator, and morning light exposure anchors the rhythm that makes falling asleep on time possible.
Frequently asked questions
- How does the Sleep Calculator work?
- Find the best bedtime or wake-up time based on sleep cycles.
- Is the Sleep Calculator free to use?
- Yes. The Sleep Calculator is completely free, runs entirely in your browser, and requires no account or sign-up. Your inputs never leave your device.
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