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Sleep Calculator

Find the best bedtime or wake-up time based on 90-minute sleep cycles

What time should I go to sleep?

How Much Sleep Do You Need?

Age GroupRecommended SleepCycles
Newborn (0–3 mo)14–17 hours9–11
Infant (4–11 mo)12–15 hours8–10
Toddler (1–2 yr)11–14 hours7–9
Preschool (3–5 yr)10–13 hours6–8
School Age (6–13 yr)9–11 hours6–7
Teen (14–17 yr)8–10 hours5–6
Adult (18–64 yr)7–9 hours5–6
Older Adult (65+)7–8 hours4–5

Source: National Sleep Foundation guidelines. One sleep cycle ≈ 90 minutes.

Frequently Asked Questions

How does the sleep calculator work?
Sleep cycles last approximately 90 minutes each, passing through light sleep, deep sleep, and REM sleep. This calculator suggests times that fall at the end of a complete cycle, so you wake up feeling refreshed rather than groggy mid-cycle.
How many hours of sleep do I need?
Adults (18–64) need 7–9 hours per night (5–6 complete cycles). Teenagers need 8–10 hours. Children 6–13 need 9–11 hours. Older adults need 7–8 hours.
Why do I feel groggy even after 8 hours of sleep?
You likely woke up in the middle of a sleep cycle. This causes "sleep inertia" — the grogginess and disorientation that can last 30–90 minutes. Use this calculator to find a wake time at the end of a complete 90-minute cycle.
What is REM sleep?
REM (Rapid Eye Movement) sleep is the deepest stage of sleep where most dreaming occurs. It's critical for memory consolidation, learning, and emotional regulation. Each sleep cycle ends in a REM stage, which gets longer through the night.