The 4 Stages of Sleep Explained
Every night, your body cycles through four key stages of sleep. Each stage has a unique purpose — from helping your muscles recover to consolidating your memories. Together, they form repeating sleep cycles that last about 90 minutes each.
🕒 Sleep Cycle Timeline
Click a stage to learn more.
Quick Overview of the Sleep Stages
Each stage is shown in the colored timeline above:
- Stage 1 Sleep – The lightest stage of sleep. This transition phase only lasts a few minutes as you drift off.
- Stage 2 Sleep – Light sleep deepens. Heart rate slows, body temperature drops, and your brain begins to produce sleep spindles.
- Stage 3 Sleep – Known as deep sleep or slow-wave sleep. It’s critical for physical repair and immune function.
- REM Sleep – The dream stage. Your brain is highly active, consolidating learning and memory while your body rests.
📊 Sleep Cycle Stage Distribution
Here’s how the proportions of each sleep stage typically change throughout the night:
| Cycle | Stage 1 | Stage 2 | Stage 3 | REM |
|---|---|---|---|---|
| 1 (~90 min) | 5% | 50% | 30% | 15% |
| 2 (~90 min) | 5% | 55% | 20% | 20% |
| 3 (~90 min) | 5% | 60% | 10% | 25% |
| 4 (~90 min) | 5% | 60% | 5% | 30% |
| 5 (~90 min, optional if long night) | 5% | 65% | 0% | 30%+ |
Brain Waves in Sleep
Each stage of sleep is marked by a different pattern of brain activity. In light sleep, theta waves dominate. In deep sleep, delta waves take over. During REM sleep, brain activity looks surprisingly similar to being awake. Learn more in Brain Waves During Sleep.
Why Sleep Stages Matter
Without moving through all stages of sleep, your body and mind can’t fully recover. Too little deep sleep affects your energy and immune system, while too little REM sleep can impact memory and learning.
Explore Each Stage
Use the links below to learn about each stage in more detail: