ZZZcalc.com
Bedtime calculator based on 90-minute sleep cycles
ZZZcalc.com launched on May 16, 2026.
What it does
ZZZCalc calculates the ideal time to go to bed or wake up based on 90-minute sleep cycles plus the average 14 minutes it takes to fall asleep. Most bedtime advice ignores sleep cycles entirely — waking mid-cycle causes grogginess no matter how many hours you slept. Features: bedtime calculator, wake-up calculator, shift worker mode, and nap calculator. Completely free, no account required.
Use this free sleep calculator to find the best time to wake up or go to bed based on 90-minute sleep cycles. No sign-up required.
This tool is for general sleep planning only and is not medical advice. A 20-minute power nap avoids deep sleep. A 90-minute nap completes one full sleep cycle. Your sleep isn't one continuous state — it moves through repeating cycles of light sleep, deep sleep, and REM, each lasting roughly 90 minutes. You pass through four to six of these cycles a night. The reason some mornings you spring awake clear-headed and others you feel like you've been hit by a truck — despite sleeping the same number of hours — comes down to where in a cycle your alarm goes off . Wake at the end of a cycle, in light sleep, and the transition to being awake is smooth. Wake in the middle of deep sleep and you get…from zzzcalc.com
Does a similar job
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Best Time For BedMay 2026 · besttimeforbed.com · ▲2Find your perfect bedtime based on 90-minute sleep cycles
Sleep Calculator2025 · openmagic-data.com · ▲7I built Sleep Calculator to help people improve sleep quality by aligning with natural 90-minute sleep cycles. You can either: Enter your desired wake-up time to get ideal times to fall asleep, or Enter your bedtime to find optimal wake-up times.
Free Sleep Calculator2025 · sleepcalculators.org · ▲6Free sleep calculator and sleep cycle calculator to find your optimal bedtime and wake-up time. Calculate your REM sleep cycles for better rest and energy
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