Sleep Calculator
Find bedtimes or wake-up times that line up with whole 90-minute sleep cycles.
A sleep calculator times your night around 90-minute sleep cycles so the alarm is more likely to go off at the end of a cycle than in the middle of deep sleep. To wake at 7:00 AM, allowing 15 minutes to fall asleep, go to bed at 9:45 PM for six cycles (9 hours) or 11:15 PM for five (7.5 hours). Four cycles, from 12:45 AM, gives only 6 hours, less than most adults need.
This calculator gives general timing suggestions based on an average 90-minute sleep cycle. It does not measure your sleep and it is not medical advice or a diagnosis. Sleep needs and cycle lengths differ between people. If you have ongoing trouble sleeping, feel tired after a full night, snore heavily or fall asleep during the day, talk to a doctor or other qualified health professional.
Try going to bed at
- 9:45 PM6 cycles, 9 hours asleep
the night before - 11:15 PM5 cycles, 7.5 hours asleep
the night before - 12:45 AM4 cycles, 6 hours asleep
short night, same day - 2:15 AM3 cycles, 4.5 hours asleep
short night, same day
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About the Sleep Calculator
Through the night you move through repeating cycles of lighter sleep, deep sleep and dream (REM) sleep, and on average one cycle lasts about 90 minutes. Waking at the end of a cycle, when sleep is lighter, tends to feel easier than being pulled out of deep sleep partway through. This calculator counts back from your alarm, or forward from your bedtime, in whole cycles, and adds the minutes you usually take to drop off, 15 by default. It shows six, five, four and three cycles, which is 9, 7.5, 6 and 4.5 hours of actual sleep. Only the first two reach the seven hours or more that most adults are advised to get, so the shorter options are marked as short nights rather than suggested. Treat the times as a rule of thumb. Real cycles vary from about 70 to 120 minutes, get longer toward morning, and differ from person to person, so no calculator can tell you when your own cycles end. If a time feels wrong for you, move it by 15 minutes and see how you wake.
Frequently asked questions
How long is a sleep cycle?+
About 90 minutes on average, which is the figure this calculator uses. Individual cycles can run from roughly 70 to 120 minutes, and REM periods tend to lengthen in the second half of the night, so the 90-minute count is a convenient average rather than a precise clock.
What time should I go to bed to wake up at 6 AM?+
With 15 minutes to fall asleep, 8:45 PM gives six cycles (9 hours) and 10:15 PM gives five cycles (7.5 hours). Going to bed at 11:45 PM would give four cycles, only 6 hours of sleep.
Is 7.5 hours of sleep better than 8 hours?+
Not necessarily. Five full cycles line up neatly on paper, but the total amount of sleep matters more than hitting an exact cycle boundary, and your cycles may not be 90 minutes long. If eight hours leaves you feeling rested, there is no reason to cut it short to match the calculator.
Why does the calculator add 15 minutes?+
Most people take a while to fall asleep after getting into bed, and 15 minutes is a common figure. The cycles are counted from when you fall asleep, not when you lie down. Change the number if you know you usually drift off faster or slower.
Can timing my sleep fix feeling tired all the time?+
Timing can make mornings a little easier, but it cannot make up for too little sleep. If you get seven hours or more and still feel unrested, snore loudly, stop breathing in your sleep or nod off during the day, talk to a doctor, because those can point to a sleep disorder that timing will not solve.
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Free to use on your own site. Paste this snippet where you want the sleep calculator to appear — it resizes itself automatically.
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</script><a href="https://manytools.co/health/sleep-calculator">Sleep Calculator by ManyTools</a>