Free sleep calculator
Sleep calculator: when should you go to bed?
Enter the time you want to wake up. You get bedtimes that fit whole sleep cycles, plus a simple light plan for your evening and morning.
This calculator needs JavaScript. Turn it on in your browser to see your times.
- Based on 90-minute cycles
- With a light plan
- Nothing is stored
Method
How the calculator works
During the night you go through several sleep cycles of light sleep, deep sleep and dream sleep. A cycle lasts about 90 minutes on average. Being woken from deep sleep often leaves you groggy for longer.
The calculator counts back from your wake-up time in average cycles of 90 minutes and adds the time you need to fall asleep. That is a rule of thumb, not a measurement of your sleep. What matters most is getting enough sleep: for most adults 7 to 9 hours, which is 5 or 6 cycles.
The light plan follows international recommendations for indoor light from 2022: plenty of light during the day, dimmed light in the three hours before bedtime and darkness while you sleep.
Sources
- Hirshkowitz M, Whiton K, Albert SM, et al. National Sleep Foundation’s sleep time duration recommendations: methodology and results summary. Sleep Health 2015;1(1):40-43.
- Watson NF, Badr MS, Belenky G, et al. Recommended amount of sleep for a healthy adult: a joint consensus statement of the American Academy of Sleep Medicine and Sleep Research Society. J Clin Sleep Med 2015;11(6):591-592.
- Brown TM, Brainard GC, Cajochen C, et al. Recommendations for daytime, evening, and nighttime indoor light exposure to best support physiology, sleep, and wakefulness in healthy adults. PLoS Biol 2022;20(3):e3001571.
- Ohayon M, Wickwire EM, Hirshkowitz M, et al. National Sleep Foundation’s sleep quality recommendations: first report. Sleep Health 2017;3(1):6-19.
Frequently asked questions
How long is a sleep cycle?
On average about 90 minutes, but it varies between people and during the night, from roughly 70 to 120 minutes. Early in the night you get more deep sleep, towards the morning more dream sleep.
How much sleep do I need?
Sleep experts advise 7 to 9 hours a night for adults up to 64 and 7 to 8 hours from 65. Teenagers need 8 to 10 hours. How rested you feel during the day is the best check.
Why do I feel groggy when the alarm goes off?
If your alarm goes off during deep sleep, it takes longer to feel fully awake. Because cycles vary, counting in 90-minute blocks is only a rough guide. A fixed wake-up time and daylight soon after getting up make mornings easier for many people.
What does light have to do with sleep?
Light sets your body clock. Bright light in the morning and during the day signals daytime to your body; dim light in the evening and darkness at night signal that night is coming.
Are my times stored?
No. The calculator runs in your browser and does not store or send your times.
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