Sleep Calculator

Calculate the best time to go to bed or wake up based on 90-minute sleep cycles. Get 4-6 optimal options and wake up feeling refreshed between cycles.

:
5 min45 min

Sleep Cycle Phases

Stage 1 (Light sleep): Transition from wakefulness, easily awakened (~5 min)
Stage 2 (Light sleep): Heart rate slows, body temperature drops (~20 min)
Stage 3 (Deep sleep): Restorative phase, tissue repair, immune boost (~20 min)
REM Sleep: Dreams occur, memory consolidation, brain activity increases (~45 min)

You should go to bed at one of these times:

9:45 PM
6 cycles · 9h of sleep
ideal
11:15 PM
5 cycles · 7.5h of sleep
good
12:45 AM
4 cycles · 6h of sleep
fair
2:15 AM
3 cycles · 4.5h of sleep
poor

Tip: For the best sleep quality, aim for 5-6 complete cycles (7.5-9 hours). Waking up at the end of a cycle, during light sleep, helps you feel more alert and refreshed.

How to Use the Sleep Calculator

  1. Choose whether you want to calculate a bedtime or wake-up time.
  2. Enter the time you need to wake up (or when you are going to bed).
  3. Adjust the "time to fall asleep" if needed (default is 15 minutes).
  4. View 4 optimal times calculated from 3-6 full sleep cycles.

Understanding Sleep Cycles

A complete sleep cycle lasts about 90 minutes and includes light sleep, deep sleep, and REM (Rapid Eye Movement) sleep. Waking up between cycles rather than during one helps you feel more refreshed. Most adults need 5-6 complete cycles (7.5-9 hours) for optimal rest.

Features

  • Calculate bedtime from wake-up time or vice versa
  • 4 options covering 3 to 6 complete sleep cycles
  • Adjustable time to fall asleep
  • Quality rating for each option
  • 100% client-side processing for full privacy
  • No data stored, no sign-up required