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Sleep Calculator

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

You should go to bed at one of these times (includes ~14 min to fall asleep):

What is a Sleep Calculator?

A sleep calculator helps you find the optimal time to go to bed or wake up based on 90-minute sleep cycles. Each cycle includes light sleep, deep sleep, and REM sleep stages. Waking up at the end of a cycle — rather than in the middle — leaves you feeling refreshed. The average person takes about 14 minutes to fall asleep, which our calculator accounts for.

How to Use

  1. Choose mode: Wake-up time (enter your desired wake time, see bedtimes) or Sleep Now (see optimal alarm times from the current moment).
  2. Results show 6 options — 2 to 6 sleep cycles (3–9 hours).
  3. Green options (5–6 cycles, 7.5–9 hours) are recommended for adults.

Frequently Asked Questions

The CDC and sleep experts recommend 7–9 hours per night for adults aged 18–64, and 7–8 hours for adults 65+. Teenagers need 8–10 hours, school-age children 9–12 hours, and toddlers 11–14 hours. Chronic sleep deprivation is linked to obesity, heart disease, and mental health problems.

A sleep cycle lasts approximately 90 minutes and includes 4 stages: N1 (light sleep, 5–10 min), N2 (intermediate sleep, 20 min), N3 (deep/slow-wave sleep, 20–40 min), and REM sleep (dreaming, 10–60 min). The proportion of REM increases in later cycles. Waking mid-cycle causes grogginess (sleep inertia).

The best bedtime depends on your required wake time. For a 7am wake-up with 7.5 hours of sleep, bedtime would be 11:16pm (accounting for 14 min to fall asleep). Most adults naturally feel sleepy between 10pm–12am due to circadian rhythms. Consistency matters more than the exact time — going to bed and waking at the same time each day improves sleep quality.

Gradually shift your sleep time by 15–30 minutes earlier or later each day. Keep a consistent schedule even on weekends. Avoid bright screens 1 hour before bed, limit caffeine after 2pm, keep your bedroom cool (65–68°F / 18–20°C), and get morning sunlight to reset your circadian clock. Avoid naps longer than 20 minutes after 3pm.

Quick Facts

  • ✓ Based on 90-min sleep cycles
  • ✓ Accounts for 14 min to fall asleep
  • ✓ Shows 6 time options per mode
  • ✓ Highlights recommended 7.5–9 hrs
  • ✓ 100% free, no login needed

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