😴 Sleep Tool
Sleep Cycle Calculator
Wake up refreshed, not groggy. Find the perfect bedtime or wake-up time based on 90-minute sleep cycles — the science of better mornings.
What would you like to calculate?
Time to fall asleep
14 minutes
—Fall asleep
—Best duration
—Best cycles
Best times to sleep
Each row = 1 more 90-min cycle
Sleep phases in one cycle (90 min)
Light sleep (N1/N2)
Deep sleep (N3)
REM sleep
✨ Tips for better sleep
Put screens away 30–60 minutes before bed. Blue light suppresses melatonin production, delaying sleep onset.
Keep your room between 16–19°C (60–67°F). A cooler room mimics your body's natural temperature drop during sleep.
Maintain a consistent sleep schedule — even on weekends. Your circadian rhythm thrives on regularity.
How sleep cycles work
Your sleep is not a single continuous state — it cycles through distinct phases roughly every 90 minutes. Each complete cycle is essential for physical recovery, memory consolidation, and emotional regulation.
The four stages of sleep
N1 — Light Sleep
1–7 min. Transition from waking. Easy to wake up; brief muscle twitches common.
N2 — Light Sleep
10–25 min. Heart rate slows, body temperature drops. Sleep spindles occur.
N3 — Deep Sleep
20–40 min. Hardest to wake from. Essential for physical repair, immune function, and growth hormone release.
REM Sleep
10–60 min (longer in later cycles). Vivid dreams. Critical for memory consolidation, learning, and emotional processing.
Frequently asked questions
How long is a sleep cycle?
A complete sleep cycle lasts approximately 90 minutes and includes light sleep, deep sleep, and REM sleep. Most adults complete 4–6 cycles per night, totalling 6–9 hours.
Why wake up at the end of a cycle?
Waking during deep sleep (N3) causes sleep inertia — grogginess and cognitive impairment. Waking at the end of a cycle, during light sleep, means your body is naturally transitioning toward waking, so you feel alert and refreshed.
How long does it take to fall asleep?
The average person takes about 14 minutes to fall asleep. This is called sleep latency or sleep onset time. This calculator uses 14 minutes as the default, which you can adjust with the slider.
How many sleep cycles do I need?
Most adults need 5–6 sleep cycles (7.5–9 hours) for optimal health. 4 cycles (6 hours) is a minimum for most people. Athletes, teenagers, and during illness may need 6+ cycles.
What is REM sleep?
REM (Rapid Eye Movement) sleep is the stage during which vivid dreaming occurs. It is essential for memory consolidation, learning, and emotional processing. REM periods get longer throughout the night, which is why the final hours of sleep are especially valuable.
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