Sleep Cycle Calculator
Calculate the best time to wake up or go to sleep based on 90-minute sleep cycles. Optimize your sleep for feeling refreshed.
About this calculator
Sleep happens in cycles of about 90 minutes, and waking up in the middle of one leaves you groggy. This calculator works out the best times to go to bed so that you wake up at the end of a cycle, feeling more refreshed.
Enter the time you need to wake up and you get a list of bedtimes, each giving a full number of cycles. Five to six cycles, or 7.5 to 9 hours, is the target for most adults. The tool adds 14 minutes, the average time to fall asleep.
How to use it
- Set the time you want to wake up and press I want to wake at…, or set a bedtime and press I want to sleep at….
- Read the list. Each row shows the cycles and total sleep.
- Choose one marked Recommended for the most rested wake-up.
Sleep cycle arithmetic
Bedtime = Wake time − (Cycles × 90 minutes) − 14 minutes. Cycles of 6, 5, 4 and 3 give 9, 7.5, 6 and 4.5 hours. Each cycle moves through light sleep, deep sleep and REM sleep.
Worked example
Waking at 6:30 am
| 21:16 | 6 cycles (9 hours), recommended |
| 22:46 | 5 cycles (7.5 hours), recommended |
| 00:16 | 4 cycles (6 hours), good |
| 01:46 | 3 cycles (4.5 hours), minimum |
| 03:16 | 2 cycles (3 hours), too little |
| 04:46 | 1 cycle (1.5 hours), too little |
Aim for the first two rows. Six hours or fewer is a regular shortfall for most adults. Times use the 24-hour clock.
Tips and common mistakes
- Keep a fixed wake-up time, even at weekends.
- Dim lights and avoid screens for an hour before bed.
- Keep the bedroom cool, dark and quiet.
- Avoid caffeine after early afternoon.
- See a doctor if you snore loudly, stop breathing at night or feel tired despite enough sleep.
Frequently asked questions
How long is a sleep cycle?
About 90 minutes, though it varies from 80 to 110.
How many hours of sleep do adults need?
Seven to nine hours.
Why add 14 minutes?
It is the typical time to fall asleep.
Is a nap a good idea?
A 20-minute nap or a full 90-minute cycle avoids deep-sleep grogginess.
Does the calculator work for children?
Children need more sleep. Their cycles are shorter.
What if I wake at night?
Brief waking between cycles is normal.