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Sleep calculator
Sleep runs in cycles of about 90 minutes, and you wake up less groggy at the end of one. Enter the time you need to get up and the calculator gives bedtimes for 9, 7.5 and 6 hours of sleep, allowing 15 minutes to fall asleep. Coming off a night shift? Use the second calculator with the time you get into bed.
By Asier Fernández ·
I have to wake up at…
I'm going to bed at… (after a night shift)
How much sleep do adults need?
The CDC recommends 7 or more hours a day for adults aged 18 to 60, 7 to 9 hours from 61 to 64 and 7 to 8 hours from 65 (CDC). Five cycles (7.5 hours) is a good target for most people; four cycles (6 hours) is a short night, fine now and then but not every day.
Why 90 minutes?
Sleep gets deeper the longer you sleep and reaches its deepest stage in about an hour. NIOSH explains that waking from deep sleep brings “sleep inertia”, grogginess that can last a while, and that waking at about 90 minutes, at the predicted end of a sleep cycle, usually means less of it (NIOSH). Cycles vary from person to person, so treat the times as a guide and adjust by 15 minutes if you still wake up tired.
Sleeping after a night shift
After nights, the hardest part is sleeping in daylight. Go to bed as soon as you can after you get home, make the room dark and cool, and keep the same sleep window for every night of the run. For people on day schedules, NIOSH recommends a brief nap of under 20 minutes, with an alarm set for 15 to 30 minutes: it raises alertness for a couple of hours with little grogginess. Whatever your shift, waking up before you reach deep sleep, or after a full cycle of about 90 minutes, is what keeps the grogginess short.
Plan the swap back to days too: the first day off after a run of nights is partly a recovery day. See swing shift schedules for rotations that change between days and nights, and the clock change dates if you work through one.
More guides
Figures are worked out from each cycle; rules checked against official sources on . How we calculate
Questions
What time should I go to bed if I wake up at 6:30?
For 7.5 hours of sleep (five cycles), at 10:45 p.m. For 9 hours, at 9:15 p.m., and for 6 hours, at 12:15 a.m. These times include 15 minutes to fall asleep.
How long is a sleep cycle?
About 90 minutes on average. NIOSH notes that waking at about 90 minutes, at the end of a cycle, usually means less grogginess.
How many hours of sleep do adults need?
7 or more hours a day for adults aged 18 to 60, according to the CDC.
How should I sleep after a night shift?
Go to bed soon after you get home, keep the room dark and cool and sleep at the same times on each day of the run. Plan for at least 7 hours.
How long should a nap be?
NIOSH says both short naps (15 to 30 minutes) and longer ones can increase alertness. Waking at about 20 minutes, before deep sleep, or at about 90 minutes, at the end of a cycle, means less grogginess.