Sleep Time Calculator
Calculate recommended bedtimes aligned to 90-minute sleep cycles based on your wake time.
Category: Date & Time
When to use?
Use it to see candidate bedtimes aligned to 90-minute sleep cycles based on when you need to wake up tomorrow.
How to use
- Enter your wake time.
- Enter how long it takes you to fall asleep, in minutes.
- See bedtimes for 6, 5, and 4 cycles.
Input Explanation
Enter the time to fall asleep as 0 to 120 minutes.
Calculation Basis
It treats a sleep cycle as 90 minutes and subtracts the cycle sleep time and fall-asleep time backward from the wake time.
Usage Examples
- Check candidate bedtimes - Compare good bedtimes based on your wake time.
- Align to sleep cycles - Pick a bedtime that lets you wake refreshed on a 90-minute cycle.
- Review your routine - Gauge the bedtime you need for your desired wake time.
Examples
- Wake 07:00, 15 min to fall asleep → 6-cycle bedtime 21:45
- Wake 06:00, 15 min to fall asleep → 5-cycle 22:15, 6-cycle 20:45
Cautions
- Sleep cycles vary by individual, so use this as a reference only.
- Time-zone settings can cause a one-day difference in some cases.
FAQ
Is this medically precise?
No. It is a reference based on 90-minute sleep cycles.
Why 90-minute units?
Sleep cycles through light and deep stages about every 90 minutes; waking in light sleep at a cycle's end is said to feel more refreshing.
Is fall-asleep time considered?
Yes, it factors in your typical time to fall asleep when suggesting bedtimes.
How many cycles should I sleep?
Adults are usually recommended 5–6 cycles (about 7.5–9 hours), but it varies by person.
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