Sleep Calculator

Calculate the best times to sleep and wake up based on 90-minute sleep cycles. Wake up feeling refreshed by aligning with your natural sleep cycles.

What time do you want to wake up?

Average is 14 minutes. Adjust if you fall asleep faster or slower.

How sleep cycles work

Sleep occurs in cycles of approximately 90 minutes each. A full cycle progresses through four stages:

  1. N1 (Light sleep): The transition between wakefulness and sleep, lasting a few minutes.
  2. N2 (Moderate sleep): Heart rate slows and body temperature drops. This stage makes up the largest portion of sleep.
  3. N3 (Deep sleep): The most restorative stage. Hard to wake from; causes grogginess if interrupted.
  4. REM (Dream sleep): Brain activity increases, dreaming occurs, and memory consolidation happens.

Waking up between cycles (during light sleep) helps you feel alert instead of groggy. This calculator times your alarm to the end of a complete cycle.

The average person takes about 14 minutes to fall asleep, which is factored into the calculations.

Frequently Asked Questions

How long is a sleep cycle?▾
A single sleep cycle lasts about 90 minutes and includes stages of light sleep, deep sleep, and REM sleep. Most adults need 5 to 6 full cycles (7.5 to 9 hours) per night for optimal rest.
Why do I feel groggy when I wake up?▾
Waking up in the middle of a sleep cycle, especially during deep sleep, causes sleep inertia (grogginess). This calculator helps you time your alarm to the end of a cycle so you wake up during lighter sleep.
How long does it take to fall asleep?▾
The average person takes about 14 minutes to fall asleep, which is factored into this calculator by default. If you fall asleep faster or slower, you can adjust this value.
What is the best time to go to sleep?▾
The best bedtime depends on when you need to wake up. Work backwards in 90-minute cycles from your alarm time and add 14 minutes to fall asleep. This calculator does the math for you.
Is this sleep calculator free to use?▾
Yes. This sleep calculator is completely free, runs entirely in your browser, and requires no signup or account. No data is sent to any server.