Sleep Calculator

Plan bedtimes or wake-up times that line up with complete 90-minute sleep cycles.

min
min
About 90 minutes for most adults

How to use the Sleep Calculator

  1. Choose the i want to.
  2. Enter the wake-up time.
  3. Enter the bedtime.
  4. Enter the time to fall asleep.
  5. Enter the sleep cycle length – About 90 minutes for most adults.
  6. Press Calculate. The result updates automatically as you type.

About the Sleep Calculator

During the night you pass through repeating sleep cycles of light sleep, deep sleep and REM sleep, each lasting roughly 80–110 minutes and averaging about 90. Waking at the end of a cycle, when sleep is lightest, tends to feel easier than being pulled out of deep sleep by an alarm.

Five or six full cycles (7.5 or 9 hours) fit the 7–9 hours most adults need. Teenagers need more, about 8–10 hours. Cycle length varies from person to person and through the night, so treat the times as a starting point and adjust the cycle length if you consistently wake before your alarm.

A consistent sleep and wake time, a dark, cool room and limiting caffeine late in the day matter more than precise timing. This is general guidance, not medical advice; talk to a doctor about persistent sleep problems.

Formula

Bedtime = Wake time − Time to fall asleep − Cycles × Cycle length
Wake time = Bedtime + Time to fall asleep + Cycles × Cycle length

Example: to wake at 6:30 AM with 15 minutes to fall asleep, 5 cycles of 90 minutes means going to bed at 6:30 − 0:15 − 7:30 = 10:45 PM.

Example calculation

Using the default values:

  • I want to = Wake up at a set time
  • Wake-up time = 06:30
  • Time to fall asleep = 15 min
  • Sleep cycle length = 90 min

the calculator returns:

  • Best time: Go to bed at 9:15 PM or 10:45 PM
  • Shorter option: 12:15 AM (6 h of sleep)

Frequently asked questions

How long is a sleep cycle?

About 90 minutes on average, typically ranging from 80 to 110 minutes.

What time should I go to bed to wake up at 6:30?

With 15 minutes to fall asleep, aim for 9:15 PM (6 cycles) or 10:45 PM (5 cycles).

Is 6 hours of sleep enough?

For most adults, no. Sleep experts recommend at least 7 hours a night for long-term health.

Last updated: · Category: Everyday Life calculators

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