Sleep Cycle Calculator
Find the best bedtime or wake-up time based on 90-minute sleep cycles. Wake up refreshed every time.
About this calculator
The Sleep Cycle Calculator tells you what time to go to bed to wake up at a given time, or what time to wake up if you go to bed now. Each suggestion is a whole number of 90-minute cycles, so you surface from light sleep instead of deep sleep.
The list starts with the earliest bedtime (six cycles, nine hours) and runs down to the latest (one cycle). Options with five or more cycles are marked with a star as the recommended choices.
How to use it
- Choose whether you want a Bedtime for a set wake-up time or a Wake-up time from now.
- Enter the time.
- Press Find Bedtimes (or Find Wake-up Times) and read the list.
Cycles
Time = Target ± (Cycles × 90 min). Healthy adults need five or six cycles. Waking during deep sleep, which dominates early cycles, causes sleep inertia, so cycle-aligned alarms feel easier.
Worked example
Waking at 7:00 am
| 9:46 pm | 6 cycles (9 hours) ⭐ |
| 11:16 pm | 5 cycles (7.5 hours) ⭐ |
| 12:46 am | 4 cycles (6 hours) |
| 2:16 am | 3 cycles (4.5 hours) |
| 3:46 am | 2 cycles (3 hours) |
| 5:16 am | 1 cycle (1.5 hours) |
Times include a 14-minute allowance for falling asleep.
Tips and common mistakes
- Choose a bedtime with at least five cycles most nights.
- If you cannot sleep, get up and do something quiet instead of watching the clock.
- Morning light helps fix your body clock.
- Do not rely on catching up at weekends.
- Alcohol fragments sleep even if it helps you drop off.
Frequently asked questions
What is a sleep cycle?
A pattern of light, deep and REM sleep lasting about 90 minutes.
How many cycles should I get?
Five to six per night for most adults.
Why do I feel tired after eight hours?
You may have woken mid-cycle, or have poor quality sleep.
Does the tool diagnose sleep disorders?
No.
What if I wake in the night?
Brief waking is normal.
Is a bedtime calculator accurate?
It is an estimate. Cycles vary between people and nights.