How long is a sleep cycle?

A typical sleep cycle lasts about 90 minutes (ranging from 70 to 120 minutes). It moves through light sleep, deep sleep, and finally REM (Rapid Eye Movement) sleep before starting over.

Why do I feel tired even after 8 hours?

If your alarm goes off in the middle of deep sleep (Stage 3), you will experience 'sleep inertia'—that heavy, groggy feeling. Waking up at the end of a 90-minute cycle (e.g., after 7.5 hours or 9 hours) is often better than 8 hours if the 8-hour mark hits mid-cycle.

What is the best temperature for sleep?

Science suggests a cool room, around 65°F (18.3°C), signals your body that it is time to rest. Your core body temperature must drop to initiate sleep.

How long is a power nap?

Aim for 10-20 minutes. This keeps you in Stage 1/2 light sleep. If you sleep 30-60 minutes, you enter deep sleep and will wake up feeling worse (groggy). If you need a long nap, go for the full 90 minutes.

The 90-Minute Rule: Stop Waking Up Tired

Sleep is not a straight line; it is a rollercoaster of brain waves. Timing your exit is the difference between feeling energized and feeling like a zombie.

Calculate Your Bedtime

Need to wake up at 7:00 AM? We'll tell you exactly when to go to sleep to hit a cycle break.

Sleep Calculator

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The Sleep Architecture: It's Not All The Same

When you close your eyes, you don't just "turn off." Your brain descends into a series of distinct stages, known collectively as a Sleep Cycle.

Stage 1 (NREM-1): The Drift
Duration: 1-5 minutes
You are just drifting off. Muscle twitching (hypnic jerks) happens here. You can be awakened easily.

Stage 2 (NREM-2): Light Sleep
Duration: 10-60 minutes
Your body temperature drops, muscles relax, and heart rate slows. Brain waves slow down. You spend about 50% of the night here.

Stage 3 (NREM-3): Deep Sleep (The "Coma")
Duration: 20-40 minutes
This is the most critical stage for physical recovery. HGH (Human Growth Hormone) is released. Waking up from this stage causes severe sleep inertia (grogginess).

REM (Rapid Eye Movement): Dreaming
Duration: 10-60 minutes
Brain activity spikes to near-waking levels. Your eyes dart around (hence the name), but your muscles are paralyzed (so you don't act out dreams). This stage is crucial for memory, learning, and mood.

The Math of Timing: The 90-Minute Rule

One full cycle (Stage 1 to REM) takes approximately 90 minutes. To wake up feeling refreshed, you want your alarm to go off at the end of a cycle, when you are in light sleep or just finishing REM.

If you wake up in the middle of a cycle (Deep Sleep), your brain is in "delta wave" mode. Dragging yourself out of delta sleep is like trying to start a cold engine.

Ideal Sleep Durations

Cycles	Duration	Verdict
4 Cycles	6.0 Hours	Minimum functional amt.
5 Cycles	7.5 Hours	The Gold Standard.
6 Cycles	9.0 Hours	Great for athletes/recovery.

Calculating Your Bedtime

Let's work backward.
Goal Wake Time: 7:00 AM

For 7.5 hours (5 cycles): Sleep at 11:30 PM.
For 9 hours (6 cycles): Sleep at 10:00 PM.

Important: The average person takes 14 minutes to fall asleep (Sleep Latency). If you get in bed at 11:30 PM, you won't fall asleep until 11:45 PM.
Fixed Plan: If you want 7.5 hours of sleep by 7:00 AM, be in bed by 11:15 PM.

The Art of the Power Nap

Napping is a double-edged sword.

The "Safe" Nap (10-20 min): You stay in Stage 1/2. You wake up refreshed, alert, and ready to go.
The "Danger" Nap (30-60 min): You enter Stage 3 (Deep Sleep). If you wake up now, you will feel groggy for an hour ("Sleep Drunkenness").
The "Full Reset" Nap (90 min): You complete a full cycle. This is great for recovery, but takes a lot of time.

The Coffee Nap Hack / "Nappuccino"

Caffeine takes about 20 minutes to metabolize and block adenosine receptors in your brain.
Step 1: Drink a cup of coffee ideally quickly (iced helps).
Step 2: Immediately set an alarm for 20 minutes and close your eyes.
Step 3: Wake up.
The result? You wake up exactly as the caffeine kicks in, stacking the benefits of sleep restoration + caffeine alert.

Sleep Hygiene Checklist

✅ Darkness: Even a tiny LED light can suppress melatonin. Use blackout curtains or an eye mask.
✅ Temperature: Cool room (65-68°F).
✅ No Blue Light: Put the phone away 1 hour before bed. Blue light mimics the sun.
✅ The Sun: Get sunlight in your eyes within 30 minutes of waking up. This sets your Circadian Rhythm for the next night.