Sleep Calculator

Suggested bedtimes — fall asleep in ~14 min:

Each sleep cycle is 90 minutes. Completing full cycles helps you wake up feeling refreshed.

What is a Sleep Calculator?

A sleep calculator determines the best times to go to bed or wake up based on your sleep cycles. Instead of just counting hours, it aligns your sleep schedule with the natural 90-minute cycle your brain moves through repeatedly each night, so you wake up feeling rested rather than groggy.

How It Works

Each sleep cycle lasts approximately 90 minutes. Waking up mid-cycle leads to sleep inertia (grogginess). The calculator adds 14 minutes for the average time it takes to fall asleep:

Bedtime   = Wake time - (cycles x 90 min) - 14 min
Wake time = Bedtime + 14 min + (cycles x 90 min)
Recommended: 5-6 cycles (7.5 to 9 hours)

Example

You need to wake up at 6:30 AM and want 5 complete cycles.

  • 5 cycles x 90 min = 450 min of sleep
  • 6:30 AM - 450 min - 14 min = 10:46 PM bedtime

Tips

  • Waking at the end of a cycle (light sleep) is much easier than waking mid-cycle (deep sleep). The times this calculator shows are the sweet spots.
  • Consistency matters as much as duration. Going to bed and waking at the same time every day trains your body clock.
  • Avoid screens for 30-60 minutes before bed. Blue light suppresses melatonin and makes it harder to fall asleep within the standard 14-minute window.

Frequently Asked Questions

How many hours of sleep do adults need?

Most adults need 7-9 hours per night. 5 sleep cycles (7.5 hours) hits the middle of that range for most people. Consistent sleep under 7 hours is linked to increased risk of health issues over time.

What is a sleep cycle?

A sleep cycle lasts about 90 minutes and includes several stages: light sleep, deep sleep (slow-wave), and REM (rapid eye movement) sleep. Each stage serves a different function in memory consolidation, physical repair, and emotional regulation.

Why do I still feel tired after 8 hours of sleep?

Waking up in the middle of a deep sleep cycle often causes sleep inertia, which feels like grogginess or fogginess. If your alarm goes off mid-cycle, you may feel worse than if you had slept 30 minutes less but woken at the end of a cycle.

Are naps counted in sleep cycles?

Short naps of 10-20 minutes work well because they stay in light sleep. A 90-minute nap completes one full cycle and can be restorative. Naps between 20-60 minutes often leave you waking mid-cycle and feeling worse than before.