Sleep Cycle Calculator (Bedtime & Wake-up)

About the Sleep Cycle Calculator (Bedtime & Wake-up)

Through the night you move through repeated sleep cycles of light, deep and REM sleep, each lasting about 90 minutes on average. The idea behind a sleep-cycle calculator is to time your alarm for the end of a cycle rather than the middle of deep sleep. Enter the time you need to wake up and it lists bedtimes that give you whole cycles; enter a bedtime — or press Sleep now — and it lists wake-up times.

You can set how long you usually take to fall asleep (15 minutes by default) and your cycle length (90 minutes by default — real cycles vary). Choose your age group to see the recommended hours of sleep from the National Sleep Foundation and the American Academy of Sleep Medicine; the options that fall inside that range are marked. Nothing you enter leaves your browser.

How the times are worked out

• Bedtime = wake-up time − (number of cycles × cycle length) − time to fall asleep. For 6:30 am, 5 cycles of 90 minutes and 15 minutes to fall asleep: 6:30 − 7 h 30 min − 15 min = 10:45 pm.
• Wake-up time = bedtime + time to fall asleep + cycles × cycle length. From 10:30 pm: 10:30 + 15 min + 7 h 30 min = 6:15 am.

For adults and teenagers the list shows 3 to 6 cycles (4½ to 9 hours); for school-age children 4 to 7 (6 to 10½ hours).

What a sleep cycle is

Sleep has two basic types, non-REM and REM. You cycle through non-REM and REM sleep several times during a typical night; REM sleep first occurs about 90 minutes after falling asleep, deep (stage 3) sleep comes in longer periods during the first half of the night, and REM periods get longer towards morning (NINDS). The first non-REM–REM cycle typically lasts about 70–100 minutes and later cycles about 90–120 minutes (Carskadon & Dement).

Because real cycles vary between people and through the night, the calculator cannot tell you exactly when a cycle ends — it gives a reasonable starting point. If you often wake just before your alarm, or feel groggy at a cycle time, try a cycle length a little shorter or longer.

How much sleep do you need?

National Sleep Foundation (2015), for healthy people:

• Newborns (0–3 months) 14–17 hours · infants (4–11 months) 12–15 hours · toddlers (1–2 years) 11–14 hours · preschoolers (3–5 years) 10–13 hours
• School-age children (6–13 years) 9–11 hours · teenagers (14–17 years) 8–10 hours
• Adults (18–64 years) 7–9 hours · older adults (65+) 7–8 hours

American Academy of Sleep Medicine: infants 4–12 months 12–16 hours per 24 hours including naps, 1–2 years 11–14 hours, 3–5 years 10–13 hours (both including naps), 6–12 years 9–12 hours and 13–18 years 8–10 hours (2016); with the Sleep Research Society, adults 18–60 years 7 or more hours a night on a regular basis (2015). It makes no recommendation for babies under 4 months because normal sleep varies so widely.

The AASM and SRS note that regularly sleeping less than 7 hours is associated with weight gain and obesity, diabetes, high blood pressure, heart disease and stroke, depression and a higher risk of death, and that more than 9 hours may be appropriate for young adults, people recovering from sleep debt and people who are ill.

Sources

• National Institute of Neurological Disorders and Stroke. Brain Basics: Understanding Sleep
• Carskadon MA, Dement WC. Normal human sleep: an overview. In: Kryger M, Roth T, Dement WC, eds. Principles and Practice of Sleep Medicine. Elsevier
• Hirshkowitz M et al. National Sleep Foundation’s sleep time duration recommendations: methodology and results summary. Sleep Health 1(1):40-3, and the NSF’s How Many Hours of Sleep Do You Really Need?
• Paruthi S et al. Recommended amount of sleep for pediatric populations. J Clin Sleep Med 12(6):785-6
• Watson NF et al. Recommended amount of sleep for a healthy adult. Sleep 38(6):843-4

Limitations

• Cycle lengths differ between people and across the night; the calculator does not measure your sleep and cannot know when your cycles end.
• For babies and children up to 5 the recommendations are totals per 24 hours including naps, so the tool shows the recommended hours but no cycle times.
• The recommendations are for healthy people. If you regularly struggle to fall or stay asleep, or are very sleepy in the day, talk to a doctor — a calculator cannot treat insomnia or a sleep disorder.

Privacy

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