Sleep calculator: what time to go to bed
Bedtimes for your alarm, counted in whole sleep cycles, plus the reverse: when to wake if you go to bed now.
To wake up at 6:30 AM, get into bed at one of these times:
- 10:45 PM 22:45 in bed
- 11:00 PM 23:00 asleep
- 12:30 AM 00:30 cycle 1 ends
- 2:00 AM 02:00 cycle 2 ends
- 3:30 AM 03:30 cycle 3 ends
- 5:00 AM 05:00 cycle 4 ends
- 6:30 AM 06:30 alarm, end of cycle 5
Each dip is one 90-minute cycle, after 15 minutes to fall asleep. Your own cycles vary from person to person and night to night, so read these as the middle of a window, not an exact minute.
How the math works
The math is simple. Start from the alarm, subtract the time it takes you to fall asleep (15 minutes by default) and then subtract whole cycles of 90 minutes. Six cycles is 9 hours of sleep, five is 7 hours 30 minutes and four is 6 hours. In "going to bed now" mode the same sum runs forward.
Why 90 minutes? It is an average. The Sleep Foundation describes cycles that "last about 90 minutes each," with the first one often shorter (70 to 100 minutes) and later ones between 90 and 120 minutes, and notes that cycles "vary from person to person and from night to night." The NIH's National Institute of Neurological Disorders and Stroke (NINDS) says REM sleep "first occurs about 90 minutes after falling asleep." Use the cycle slider if you know your nights run longer or shorter.
The 15-minute default comes from the normal range for adults: the Sleep Foundation puts typical sleep latency between 10 and 20 minutes. If you usually lie awake longer, change it, and read the note at the bottom of this page.
The timeline is a picture of the arithmetic, not a measurement of your sleep. Dips get shallower toward morning because, as NINDS explains, deep sleep comes in longer periods in the first half of the night and REM periods get longer later on.
General information based on published averages, not medical advice. Sleep cycles and needs vary from person to person. If you have problems sleeping or feel unusually tired during the day, see a doctor.