Your sleep is made up of 90-minute cycles
Instead of thinking “8 hours is enough,” science says we should complete full sleep cycles.
One cycle = light sleep → deep sleep → REM (dreaming).

Waking up during a cycle? You feel tired.
Waking up in the middle of a cycle (like deep sleep) can make you feel groggy and lazy
— even after 8+ hours of sleep.

Waking up at the end of a cycle? You feel fresh.
Our calculator helps you plan bedtimes that match your sleep cycles, so you wake up at the right time — full of energy.

Each cycle lasts about 90 minutes. A healthy adult completes 4 to 6 cycles per night.
Here’s how it works:

0 – 10 mins: Stage N1 (Light Sleep)

• You’re just drifting off — a half-awake, half-asleep state.

• Breathing slows, muscles relax

10 – 25 mins: Stage N2 (Deeper Light Sleep)

• Body temperature drops, and heart rate slows.

• Brain starts blocking out external sounds.

• Makes up about 50% of your total night’s sleep.

25 – 45 mins: Stage N3 (Deep Sleep)

• This is where your body heals and recovers.

• Growth hormone is released, and immune function strengthens.

• It’s hardest to wake up during this phase.

• Most important for physical restoration.

45 – 90 mins: REM Sleep (Dreaming Stage)

• Rapid Eye Movement (REM) begins.

• Brain becomes active — dreams happen here.

• Memory consolidation and emotional processing occur.

• Muscles are temporarily “paralyzed” to prevent acting out dreams.

Sleeping 4 cycles (6 hours) is okay sometimes — but try to aim for 5 or 6 for better health.