health

Sleep Cycle

A recurring pattern of sleep stages (light, deep, REM) that repeats approximately every 90 minutes throughout the night.

A sleep cycle lasts about 90 minutes and includes four stages: N1 (light sleep), N2 (onset), N3 (deep/slow-wave sleep), and REM (rapid eye movement / dreaming).

Stage Details

  • N1 (5%): Transition from wakefulness, easily awakened
  • N2 (45%): Heart rate slows, body temperature drops
  • N3 (25%): Deep sleep — tissue repair, immune strengthening, growth hormone release
  • REM (25%): Brain is active (dreaming), memory consolidation, emotional processing

Optimal Wake Time

Waking at the end of a full cycle (rather than mid-cycle) reduces grogginess. For 5 full cycles: 7.5 hours of sleep.

Related Calculators

📊 Sleep Calculator

Related Articles

📝 Sleep Cycles Explained

Related Terms

BMI (Body Mass Index)

A numerical value calculated from height and weight, used as a screening tool for body fat categories.

BMR (Basal Metabolic Rate)

The number of calories your body burns at complete rest to maintain basic life functions.

TDEE (Total Daily Energy Expenditure)

The total number of calories burned per day, including exercise and daily activities on top of BMR.

Macronutrients

The three main nutrients the body needs in large amounts: protein, carbohydrates, and fats.

Body Fat Percentage

The proportion of total body weight that is composed of fat tissue.

Blood Pressure

The force of blood pushing against artery walls, measured as systolic over diastolic pressure.