Sleep Cycles 101: Understanding Your 90-Minute Rhythm

Sleep isn't just one long, continuous state of rest. Instead, it's composed of multiple cycles that repeat throughout the night. Each cycle lasts approximately 90 minutes and consists of different stages of sleep.

What Happens During a Sleep Cycle?

Stage 1: Light Sleep (1-7 minutes)

This is the transition phase between wakefulness and sleep. Your muscles relax, and your brain waves begin to slow down.

Stage 2: Light Sleep (10-25 minutes)

Your body temperature drops, and your heart rate slows. This stage accounts for about 50% of your total sleep time.

Stage 3: Deep Sleep (20-40 minutes)

Also known as slow-wave sleep, this is when your body repairs tissues and builds bone and muscle. It's crucial for physical recovery.

REM Sleep (10-60 minutes)

Your brain becomes more active, and this is when most dreaming occurs. REM sleep is essential for memory consolidation and emotional processing.

Why 90-Minute Cycles Matter

Completing full sleep cycles is crucial for waking up refreshed. If you wake up in the middle of deep sleep, you'll likely feel groggy and disoriented.

Calculating Your Optimal Bedtime

To determine your ideal bedtime:

Start with your target wake time
Count back in 90-minute intervals
Add 15 minutes for sleep latency (the time it takes to fall asleep)

For example, if you need to wake up at 7:00 AM:

6 cycles: 9 hours of sleep → 10:00 PM bedtime
5 cycles: 7.5 hours of sleep → 11:30 PM bedtime
4 cycles: 6 hours of sleep → 1:00 AM bedtime

Tips for Better Sleep Cycles

1. Be Consistent

Try to go to bed and wake up at the same time every day, even on weekends.

2. Create a Bedtime Routine

A consistent bedtime routine signals to your body that it's time to sleep.

3. Optimize Your Environment

Keep your bedroom cool, dark, and quiet for optimal sleep.

4. Avoid Screens Before Bed

The blue light from screens can interfere with melatonin production.