SleepyClock

睡眠计算器 睡眠周期 90分钟 几点睡几点起 | sleep calculator 90 minute cycle bedtime wake time

Sleep Calculator

Wake up refreshed — sleep in complete 90-minute cycles. Enter your wake-up time or bedtime and get instant, science-based recommendations.

Tap the time to adjust. Results update instantly.

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How it works

  1. 1

    Pick a mode — bedtime or wake-up time.

  2. 2

    Set your time — results update instantly as you type.

  3. 3

    Choose a cycle — wake at the end of a 90-minute cycle to feel refreshed.

Each sleep cycle lasts about 90 minutes. We add an average of 15 minutes for falling asleep, so the bedtime you see is the moment to get into bed.

Frequently asked questions

What is a sleep cycle?

A sleep cycle lasts about 90 minutes and includes light sleep, deep sleep and REM (dream) sleep. Waking up at the end of a cycle leaves you feeling most refreshed, which is why this calculator works in 90-minute blocks.

How many hours of sleep do I need?

Most adults need 7–9 hours (about 5–6 full sleep cycles). Teens need 8–10 hours, and young children need even more. This calculator shows options from 2 to 6 cycles (3 to 9 hours) so you can choose what works for your schedule.

How long does it take to fall asleep?

On average it takes about 15 minutes to fall asleep. The calculator adds this time, so your bedtime reflects when you should get into bed, not just when your first sleep cycle starts.

What is a power nap and when should I take one?

A power nap is a short nap of about 25 minutes that boosts alertness without entering deep sleep. A 60-minute memory nap includes deep sleep and improves memory. Naps work best when you have less than 5 hours before your target wake time.

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Scan the QR code with WeChat, or search 睡眠周期小助手 — the same sleep-cycle calculator, right on your phone.

WeChat mini program QR code — SleepyClock 睡眠周期小助手

Disclaimer: This tool is for general informational purposes only and is not medical advice. If you have chronic sleep problems, please consult a healthcare professional.