Sleep Calculator — Find Your Ideal Bedtime or Wake Time
Find the bedtime or wake time that aligns with your natural 90-minute sleep cycles. Waking at the end of a full cycle leaves you feeling refreshed instead of groggy.
Use 24-hour time: 07:00 for 7 AM, 22:30 for 10:30 PM.
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Frequently asked questions
What is a sleep cycle?
A sleep cycle is one full rotation through light sleep (stages 1–2), deep sleep (stages 3–4), and REM sleep. Cycles average 90 minutes and repeat 4–6 times per night. Deep sleep dominates the first half of the night (physical recovery); REM sleep dominates the second half (memory consolidation, mood regulation). Waking during deep sleep or mid-REM leaves you disoriented — sleep inertia can last 30+ minutes.
How much sleep do I need by age?
CDC and AASM consensus: newborns 14–17 hours, infants 12–15, toddlers 11–14, preschoolers 10–13, school-age 9–11, teens 8–10, adults 18–64 need 7–9 hours, adults 65+ need 7–8 hours. Individual variation is real but small — fewer than 1% of adults are true short sleepers who function well on under 6 hours. Most people who claim 5 hours is enough are running a sleep debt they've adapted to.
Why do I wake up tired even after 8 hours?
Most common causes: waking mid-cycle (this calculator addresses that), poor sleep quality from caffeine after noon, alcohol within 4 hours of bed, sleep apnea (snoring + daytime fatigue + morning headaches), screen exposure suppressing melatonin, irregular sleep schedule. If consistent 7.5+ hour sleep still leaves you exhausted, see a doctor — sleep apnea affects ~30 million US adults and is underdiagnosed.