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Daily Dose of Utilities

Sleep Calculator: When to Go to Bed or Wake Up

Count back in 90-minute sleep cycles from your alarm, plus about 15 minutes to fall asleep. To wake at 7:00 AM after 5 cycles (7.5 hours), go to bed at 11:15 PM; for 6 cycles (9 hours), 9:45 PM.

min

Try to fall asleep by going to bed at

  • 9:45 PM

    6 cycles · 9 hours of sleep

  • 11:15 PM

    5 cycles · 7.5 hours of sleep · recommended

  • 12:45 AM

    4 cycles · 6 hours of sleep

  • 2:15 AM

    3 cycles · 4.5 hours of sleep

Show the math

  1. 1

    Sleep comes in cycles of about 90 minutes

    6 cycles = 9 h · 5 cycles = 7.5 h · 4 cycles = 6 h

    Each cycle moves through light, deep and REM sleep. Waking at the end of a cycle, rather than in deep sleep, usually feels less groggy.

Read the steps as text
  1. Sleep comes in cycles of about 90 minutes. 6 cycles = 9 h · 5 cycles = 7.5 h · 4 cycles = 6 h Each cycle moves through light, deep and REM sleep. Waking at the end of a cycle, rather than in deep sleep, usually feels less groggy.
  2. Count back from your wake-up time. 7:00 AM − 7 h 30 min of sleep − 15 min to fall asleep = 11:15 PM Most adults need 7 to 9 hours, so 5 or 6 cycles is the goal. It takes about 15 minutes to drift off.
  3. Other bedtimes. 6 cycles → 9:45 PM · 5 cycles → 11:15 PM · 4 cycles → 12:45 AM · 3 cycles → 2:15 AM

Why sleep in 90-minute cycles

Through the night your brain moves through repeating cycles of light sleep, deep sleep and REM (dreaming) sleep, each lasting roughly 90 minutes. Being woken from deep sleep tends to leave you groggy, while waking near the end of a cycle, when sleep is lighter, usually feels easier.

The calculator adds or subtracts whole cycles from your chosen time, plus the time it takes you to fall asleep (about 15 minutes for most people). Five cycles is 7.5 hours and six is 9 hours, both within the 7 to 9 hours adults are recommended to get.

Treat the times as a guide

Real cycles vary from about 70 to 120 minutes and change through the night, with more deep sleep early on and more REM toward morning. So the times are a starting point; if you still wake groggy, try shifting your bedtime by 15 minutes either way.

Getting enough total sleep matters more than hitting a cycle boundary exactly. A regular schedule, even at weekends, plus a dark, cool room and less screen time before bed make a bigger difference than precise timing.

Frequently asked questions

What time should I go to bed to wake up at 6 AM?
For 5 cycles (7.5 hours), at about 10:15 PM; for 6 cycles (9 hours), at 8:45 PM. Both include 15 minutes to fall asleep.
How many hours of sleep do adults need?
Health organizations recommend 7 to 9 hours for adults. Teenagers need 8 to 10, and younger children more.
Is 6 hours of sleep enough?
Four complete cycles (6 hours) may feel better than 6.5 hours that ends mid-cycle, but regularly sleeping 6 hours or less is linked to poorer health and concentration for most adults.
What if I take longer to fall asleep?
Change the 'time to fall asleep' value. If it regularly takes more than 30 minutes, it may be worth talking to a doctor.

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