90 Minute Sleep Calculator

Find your ideal bedtime or wake-up time based on 90-minute sleep cycles.

Sleep Calculator Overview

Inputs:
  • Calculate (Bedtime or Wake-up Time)
  • Time (specific hour and minute)
  • Sleep Cycles (4, 5, or 6 cycles)
Output:

Recommended bedtime or wake-up times based on 90-minute sleep cycles.

Formula:

Each sleep cycle lasts 90 minutes. Add 15 minutes to fall asleep:

  • Bedtime = Wake-up Time - (Cycles × 90 min + 15 min)
  • Wake-up = Bedtime + (Cycles × 90 min + 15 min)

The calculator suggests times to align with the end of a sleep cycle.

Understanding Sleep

Why Sleep Cycles Matter

Sleep occurs in 90-minute cycles, including light sleep, deep sleep, and REM (Rapid Eye Movement) stages. Waking up at the end of a cycle—during light sleep—helps you feel refreshed and alert. Interrupting deep sleep, however, can leave you groggy and tired, a phenomenon known as sleep inertia. Our 90-minute sleep calculator ensures you wake up at the optimal time.

  • 4 Cycles (6 hours): Minimum for most adults.
  • 5 Cycles (7.5 hours): Recommended for optimal rest.
  • 6 Cycles (9 hours): Ideal for recovery or teens.

Recommended Sleep by Age

Age Group Recommended Sleep (Hours) Sleep Cycles
Newborns (0-3 months)14-179-11
Adults (18-64)7-95-6
Older Adults (65+)7-85

Use this calculator to plan your sleep, and pair it with our Calorie Calculator, Body Fat Calculator, or Water Intake Calculator for overall wellness. Learn more from the Sleep Foundation.

Frequently Asked Questions

The calculator uses 90-minute sleep cycles, the average length of one complete cycle (light, deep, REM sleep). It calculates bedtime or wake-up times by adding or subtracting cycles from your input time, including 15 minutes to fall asleep.

Waking up at the end of a sleep cycle (light sleep) helps you feel refreshed. Waking during deep sleep can leave you groggy. The calculator aligns your sleep with these natural cycles.

Adults typically need 7-9 hours, or 5-6 sleep cycles (7.5-9 hours including time to fall asleep). Our calculator lets you choose based on your preference or age group.

If you know when you need to wake up, calculate bedtime. If you’re going to bed now, calculate wake-up times. Both options optimize your sleep cycles.

Stick to a consistent sleep schedule, avoid screens before bed, and create a dark, quiet environment. Use the calculator to plan your sleep duration effectively.

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Learn more about MG Calculator on our About Us page. | Have questions? Reach out via our Contact Us page.