Sleep Calculator
Quick answer
Enter the time you need to wake up (or the time you plan to go to bed) and this calculator suggests bedtimes and wake times aligned to your natural 90-minute sleep cycles — so you wake up closer to the end of a cycle instead of mid-dream.
Last updated:
Your details
Everything runs in your browser — nothing is stored or sent anywhere.
The 90-minute cycle method
Each sleep cycle ≈ 90 minutes, repeated 4–6 times a night
Add ~15 minutes to fall asleep when planning
Wake time = bedtime + 15 min + (cycles × 90 min)
Bedtime = wake time − 15 min − (cycles × 90 min)
Most adults need 7+ hours (AASM/CDC). Waking at the end of a cycle leaves you less groggy than an alarm in deep sleep — but the best schedule is the one you can keep consistently.
Worked example
- 1
You need to wake at 6:00 AM.
- 2
5 cycles = 7.5 h of sleep. Add 15 min to fall asleep → 7 h 45 min.
- 3
Bedtime = 6:00 AM − 7 h 45 min = 10:15 PM the night before.
- 4
A 4-cycle target (6 h sleep) would mean going to bed at 11:45 PM — under the 7-hour guideline, so use it rarely.
Interpreting your sleep schedule
| Your result | Category | What it means |
|---|---|---|
| 6 cycles ≈ 9 hours | Optimal for many adults | The most generous schedule. If you are currently short on sleep or train hard, this is the recovery-friendly target. |
| 5 cycles ≈ 7.5 hours | Meets the 7-hour guideline | CDC / AASM recommend at least 7 hours for adults — 5 cycles comfortably clears that bar and fits most schedules. |
| 4 cycles ≈ 6 hours | Below the guideline | Under the recommended 7 hours. Fine occasionally, but not as a long-term habit — adults averaging less than 7 hours show higher health risks. |
The 90-minute cycle is a useful planning rule of thumb — sleep stages cycle roughly every 80–110 minutes for most people.
Frequently asked questions
Sources & further reading
Related calculators
Heart Rate Zone Calculator
Your five training zones from your age (Tanaka formula).
Open calculatorCalories Burned Calculator
Estimate calories burned per activity from Compendium MET values.
Open calculatorWater Intake Calculator
How much water to drink per day for your body and activity.
Open calculatorThis calculator provides general estimates for informational purposes only and is not medical advice. For personal guidance, consult a qualified healthcare provider.