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😴 Sleep Calculator

Find the perfect time to go to sleep or wake up based on 90-minute sleep cycles. Wake up feeling refreshed — not groggy — every single morning!

✏️ Enter Your Values
✨ Your Result
Result
🦉Owl's Explanation
😴
Fill in the values on the left
and click Calculate! ✨

🤔 How Does This Tool Work?

Our Sleep Calculator is based on the science of sleep cycles. Each sleep cycle lasts approximately 90 minutes and includes three stages:

  • Light Sleep (Stage 1 and 2) — easy to wake up from, feeling refreshed
  • Deep Sleep (Stage 3) — body repairs itself, growth hormones released
  • REM Sleep — dreaming occurs, memories are consolidated

The calculator adds 14 minutes for average time to fall asleep, then calculates times at 90-minute intervals. It shows you 6 options — the ones closest to 7.5 to 9 hours (5 to 6 cycles) are ideal for most adults.

📚 Related Article
What Time Should You Sleep Tonight? Science Has the Answer →
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❓ FAQ
What is a sleep cycle?▼
A sleep cycle is a 90-minute period that includes light sleep, deep sleep, and REM (dreaming) sleep. Adults typically complete 4 to 6 cycles per night. Waking up at the END of a cycle feels much better than waking in the middle of deep sleep.
Why does waking up mid-cycle feel so awful?▼
When you wake during deep sleep, your brain is in a state called 'sleep inertia' — it has not completed its natural cycle. This causes grogginess, confusion, and fatigue that can last hours. Waking at the end of a cycle means waking during light sleep, which feels natural.
How many sleep cycles do I need?▼
Most adults need 5 to 6 complete sleep cycles (7.5 to 9 hours) per night. Teenagers need 5 to 7 cycles (7.5 to 10.5 hours). Children need even more — 8 to 11 cycles! Quality of cycles matters as much as quantity.
Does everyone have exactly 90-minute cycles?▼
Sleep cycles typically range from 80 to 110 minutes. The 90-minute figure is the average. Our calculator uses 90 minutes as the standard, which works well for most people. Individual variation is normal.
What time should I go to sleep if I wake at 6am?▼
Based on 90-minute cycles: 10:46 PM (5 cycles — ideal!), 9:16 PM (6 cycles), or 12:16 AM (4 cycles — minimum). Add 14 minutes to account for time to fall asleep. Our calculator shows you all options!
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