Sleep Calculator

Find the best bedtime or wake-up time based on 90-minute sleep cycles

Sleep Cycle Calculator

Includes 15 minutes to fall asleep.

Best times to wake up:

4:45 AM

6h 15m of sleep

Minimum · 4 cycles

6:15 AM

7h 45m of sleep

Great · 5 cycles

7:45 AM

9h 15m of sleep

Optimal · 6 cycles

If you sleep NOW (9:44 PM):

3:59 AM

6h 15m · 4 cycles

5:29 AM

7h 45m · 5 cycles

6:59 AM

9h 15m · 6 cycles

Based on 90-minute sleep cycles. Results are estimates - individual cycles vary by 10-20 minutes. A consistent schedule matters more than perfect timing.

Frequently Asked Questions

What is a sleep cycle?

A sleep cycle lasts approximately 90 minutes and consists of several stages: light sleep (N1, N2), deep sleep (N3/slow-wave sleep), and REM (Rapid Eye Movement) sleep. Adults typically go through 4-6 cycles per night. Waking at the end of a cycle - rather than in the middle - leaves you feeling refreshed.

How many hours of sleep do I need?

Most adults need 7-9 hours per night (4-6 complete 90-minute cycles). Teenagers need 8-10 hours, school-age children 9-11 hours, and toddlers 11-14 hours. Chronic sleep deprivation (less than 6 hours) is linked to increased risk of obesity, heart disease, diabetes, and cognitive decline.

Why do I feel groggy even after 8 hours?

Grogginess (sleep inertia) usually means you woke up during a deep sleep stage, not at the end of a cycle. Try adjusting your wake time by 15-30 minutes earlier or later. This calculator helps you find times that align with cycle boundaries so you wake naturally feeling alert.

What is REM sleep and why does it matter?

REM sleep is the stage where most vivid dreaming occurs. It's critical for memory consolidation, emotional processing, and creativity. REM stages get longer as the night progresses - the first REM period lasts about 10 minutes, while the last can be an hour. Waking during REM causes the strongest grogginess.

How long does it take to fall asleep?

The average person takes 10-20 minutes to fall asleep. This calculator adds 15 minutes to your bedtime to account for this. If you fall asleep in less than 5 minutes, you may be sleep-deprived. If it consistently takes longer than 30 minutes, you may have insomnia.