Sleep Calculator

Find the ideal bedtime or wake-up time based on 90-minute sleep cycles. Waking at the end of a complete sleep cycle means you'll feel more rested and alert — rather than groggy mid-cycle.

Sleep Cycle Calculator

How Sleep Cycles Work

One sleep cycle = ~90 minutes Full night = 5–6 complete cycles = 7.5–9 hours Bedtime = Wake time − (cycles × 90 min) − fall-asleep time Wake time = Bedtime + fall-asleep time + (cycles × 90 min)

Recommended Sleep by Age

Age GroupRecommended Sleep
Newborns (0–3 months)14–17 hours
School children (6–13)9–11 hours
Teenagers (14–17)8–10 hours
Adults (18–64)7–9 hours
Older adults (65+)7–8 hours

Frequently Asked Questions

What is a sleep cycle?+
A sleep cycle lasts about 90 minutes and includes light sleep, deep sleep (slow-wave), and REM (rapid eye movement) sleep. Most adults complete 4–6 cycles per night. Waking mid-cycle can cause grogginess called "sleep inertia."
Why do I still feel tired after 8 hours of sleep?+
Waking in the middle of a deep sleep cycle can leave you groggy even after plenty of hours. Try adjusting your alarm by 15–30 minutes so you wake at the end of a complete 90-minute cycle. Sleep quality, sleep disorders, and nutrition also affect how rested you feel.

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