What time should you go to bed?
Your wake-up time, your age, your training: the bedtimes that land at the end of a sleep cycle, and your night playing out so you can see where your alarm falls.
Go to bed at
Tap a time to see your night
Your night, cycle by cycle
How it's calculated
- The questions: the time you can't move (your wake-up time, or your bedtime), your age, your training and how long you take to fall asleep. Nothing else goes into the calculation.
- One sleep cycle: we count 90 minutes, the average length you see quoted everywhere. In reality, the first cycle lasts 70 to 100 minutes and the next ones 90 to 120 (M. Carskadon and W. Dement, “Normal human sleep: an overview”, Principles and Practice of Sleep Medicine, 2005, cited by the Institute of Medicine, 2006). So it's a guide, not a clock: after five cycles, your real night can be more than half an hour off.
- Time to fall asleep: 15 minutes if you don't know. That's our typical value, in the middle of what marks good-quality sleep: falling asleep in 30 minutes or less (M. Ohayon et al., “National Sleep Foundation's sleep quality recommendations: first report”, Sleep Health, 2017).
- The times: your bedtime = your wake-up time, minus the time to fall asleep, minus a whole number of cycles. For your wake-up time it's the other way round: your bedtime, plus the time to fall asleep, plus the cycles. The subtraction across midnight is the Cadevia app's own, which also works out your bedtime from your wake-up time.
- Recommended sleep for your age: 8 to 10 hours from 14 to 17, 7 to 9 hours from 18 to 64, 7 to 8 hours from 65 (M. Hirshkowitz et al., “National Sleep Foundation's sleep time duration recommendations: methodology and results summary”, Sleep Health, 2015). These ranges are for healthy people without a sleep disorder.
- Your target sleep: 7h 30m if you train under 3 hours a week, 8h 15m from 3 to 8 hours, 8h 45m above that. It's the Cadevia app's starting point, before it learns your need from your nights: in basketball players, longer nights improved speed and shooting accuracy (C. Mah et al., “The effects of sleep extension on the athletic performance of collegiate basketball players”, Sleep, 2011). If it falls outside the range for your age, we bring it back to the nearest limit (our setting).
- The recommended time: the number of cycles that stays within the range for your age and comes closest to your target sleep. If two numbers are equally close, we take the longer one: for the same gap, we never have you sleep less than you need. “Shorter” takes off one cycle, for the nights you get to bed late.
- Easy or hard wake-up: 15 minutes or less from the end of a cycle, you wake from light sleep (easy). In the middle of one of the first two cycles, more than 20 minutes from its start and its end, you're in deep sleep, which is packed into the first third of the night (Carskadon and Dement): that's where waking up leaves you groggy the longest, what's called sleep inertia (P. Tassi and A. Muzet, “Sleep inertia”, Sleep Medicine Reviews, 2000). Anywhere else mid-cycle, waking up is less easy. The 15 and 20 minute thresholds are our setting.
- The drawing: a diagram, not your hypnogram. Each wave is a cycle that goes down toward deep sleep, then back up toward light sleep and dream (REM) sleep; the waves at the end of the night are shallower, as in a real night. The night plays out fast, from bedtime to wake-up.
- The limits: it's a guide, not a promise that you'll wake up fresh to the minute: your cycles change from one night to the next, with tiredness, alcohol, caffeine or stress. If you often take more than 30 minutes to fall asleep, or you stay tired despite long enough nights, talk to a doctor.
Frequently asked questions
What time should I go to bed to wake up at 7 AM?
At 11:15 PM for 5 cycles of 90 minutes (7h 30m of sleep), or at 9:45 PM for 6 cycles (9h), counting 15 minutes to fall asleep. The tool highlights the one that fits your age and training.
How long is a sleep cycle?
About 90 minutes on average, but it isn't a clock: the first cycle lasts 70 to 100 minutes, the next ones 90 to 120 (Carskadon and Dement). A 7h 30m night holds five.
How much sleep do you need by age?
8 to 10 hours from 14 to 17, 7 to 9 hours from 18 to 64, 7 to 8 hours from 65, according to the National Sleep Foundation (2015). The Cadevia app starts from 8h 15m for someone who trains 3 to 8 hours a week.
Why do I wake up tired after a full night's sleep?
Often because your alarm caught you mid-cycle, or even in deep sleep: that's where sleep inertia lasts longest (Tassi and Muzet, 2000). Aiming for the end of a cycle helps; if the tiredness lasts despite long enough nights, talk to a doctor.