Sleep Calculator
Sleep cycles last 90 minutes on average, cycling through NREM (stages 1-3) and REM sleep. Complete 5-6 cycles per night (7.5-9 hours). Waking mid-cycle causes grogginess. Calculate bedtime: count back 90-minute cycles from wake time, add 15 minutes to fall asleep. For 7 AM wake: 5 cycles = 11:30 PM bedtime, 6 cycles = 10:00 PM. Adults need 7-9 hours, teens 8-10 hours, children 9-12 hours. Quality matters: deep sleep (stage 3) for physical recovery, REM for memory consolidation.
Calculate optimal bedtimes or wake-up times based on 90-minute sleep cycles. Choose "wake up at" or "go to sleep at" mode, account for 15 minutes to fall asleep, and see color-coded recommendations for 3–6 sleep cycles. Includes sleep hygiene tips.
Mode
Wake-up time
Enter the time you need to wake up
Recommended bedtimes
Based on 90-minute sleep cycles + 15 minutes to fall asleep
💡 Sleep Hygiene Tips
- •Stick to a consistent sleep schedule, even on weekends.
- •Avoid screens (phone, TV, computer) for at least 30 minutes before bed.
- •Keep your bedroom cool (60–67°F / 15–19°C), dark, and quiet.
- •Avoid caffeine at least 6 hours before bedtime.
- •Exercise regularly, but not within 2–3 hours of bedtime.
- •Avoid large meals and alcohol close to bedtime.
- •Create a relaxing bedtime routine (reading, stretching, meditation).
- •Limit naps to 20–30 minutes earlier in the day.
How to Use
- Enter your value in the input field
- Click the Calculate/Convert button
- Copy the result to your clipboard
Frequently Asked Questions
- How does the sleep cycle calculator work?
- The sleep calculator uses 90-minute sleep cycles, which is the average length of one full cycle through all sleep stages (light sleep, deep sleep, and REM). It adds 15 minutes for the average time to fall asleep and calculates optimal bedtimes or wake times so you wake at the end of a cycle rather than in the middle, helping you feel more refreshed.
- Why are sleep cycles 90 minutes long?
- A complete sleep cycle lasts roughly 90 minutes and includes four stages: N1 (light sleep, 1–5 min), N2 (deeper sleep, 10–60 min), N3 (deep/slow-wave sleep, 20–40 min), and REM (dreaming, 10–60 min). The 90-minute figure is an average — individual cycles range from 70 to 120 minutes and shift throughout the night, with more deep sleep early and more REM sleep later.
- How many hours of sleep do I need?
- Adults (18–64) generally need 7–9 hours of sleep, which corresponds to 5–6 complete 90-minute cycles. Teenagers need 8–10 hours, school-age children need 9–12 hours, and older adults (65+) need 7–8 hours. Quality matters as much as quantity — waking at the end of a cycle helps you feel more rested even with the same total sleep time.
- Is it better to wake up at the end of a sleep cycle?
- Yes. Waking during deep sleep (N3 stage) causes sleep inertia — that groggy, disoriented feeling. Waking at the end of a cycle, typically during lighter sleep, helps you feel alert and refreshed. This is why sleeping 7.5 hours (5 cycles) can feel better than sleeping 8 hours if 8 hours puts you mid-cycle.
- Why does the calculator add 15 minutes?
- The 15-minute buffer accounts for the average time it takes a healthy adult to fall asleep, known as sleep onset latency. If you fall asleep faster (under 5 minutes, which may indicate sleep deprivation) or slower (over 30 minutes, which may indicate insomnia), your actual sleep time will differ slightly from the estimate.
- What are the best tips for better sleep?
- Key sleep hygiene practices include: maintaining a consistent sleep schedule (even on weekends), keeping your bedroom cool (60–67°F / 15–19°C) and dark, avoiding screens 30+ minutes before bed, limiting caffeine after noon, exercising regularly but not close to bedtime, and creating a relaxing pre-sleep routine such as reading or meditation.