Sleep Calculator
Find the best time to go to bed or wake up based on 90-minute sleep cycles. Wake up feeling refreshed by timing your sleep to complete full cycles.
Go to bed at one of these times:
9:46 PM
Recommended6 cycles
9 hours of sleep
11:16 PM
Recommended5 cycles
7.5 hours of sleep
12:46 AM
4 cycles
6 hours of sleep
Includes ~14 minutes to fall asleep. Each sleep cycle is approximately 90 minutes.
Recommended Sleep by Age (National Sleep Foundation)
The 4 Stages of a Sleep Cycle
Stage 1 (N1)
1–5 minLight sleep. Transition between wakefulness and sleep. Easy to wake up.
Stage 2 (N2)
10–25 minBody temperature drops, heart rate slows. Brain produces sleep spindles.
Stage 3 (N3)
20–40 minDeep sleep. Body repairs muscles, bones, and tissue. Strengthens immune system.
REM Sleep
10–60 minBrain is active, eyes move rapidly. Dreaming occurs. Important for memory and learning.
Tips for Better Sleep
- Keep a consistent sleep schedule, even on weekends
- Avoid screens (blue light) for 30-60 minutes before bed
- Keep your bedroom cool (60-67 degrees F / 15-19 degrees C)
- Avoid caffeine at least 6 hours before bedtime
- Exercise regularly, but not within 2-3 hours of bedtime
- Avoid large meals and alcohol close to bedtime
Frequently Asked Questions
What is a sleep cycle?
A sleep cycle lasts approximately 90 minutes and consists of 4 stages: N1 (light sleep), N2 (deeper sleep), N3 (deep/slow-wave sleep), and REM (rapid eye movement). You typically go through 4-6 complete cycles per night. Waking up between cycles (rather than in the middle of one) helps you feel more refreshed.
Why do I feel groggy even after 8 hours of sleep?
If you wake up in the middle of a deep sleep stage (N3), you experience "sleep inertia" — that heavy, groggy feeling. This calculator helps you time your sleep so you wake up at the end of a complete cycle, when you are in lighter sleep and naturally more alert.
How long does it take to fall asleep?
This calculator assumes it takes about 14 minutes to fall asleep, which is the average for healthy adults. If you tend to fall asleep faster or slower, adjust the suggested times accordingly. Taking more than 20 minutes consistently may indicate a sleep issue.
How many sleep cycles do I need?
Most adults need 5-6 sleep cycles (7.5-9 hours). Teens need about 6 cycles (9 hours). The minimum for most adults is 4 cycles (6 hours), though this is not recommended for regular use. The calculator highlights the optimal number of cycles for your age group.