📌 Overview

Find the best times to go to bed or wake up based on 90-minute sleep cycles, so you wake at the end of a cycle instead of mid-deep-sleep.

😴 Sleep Calculator

Find the best times to go to bed or wake up based on 90-minute sleep cycles, so you wake at the end of a cycle instead of mid-deep-sleep.

I want to know

Time

Minutes to fall asleep

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📋 How to Use

Choose whether you know your wake-up time or bedtime.
Set the time.
Click Calculate.
Pick one of the suggested times — later options mean more cycles.

❓ FAQ

Why 90 minutes?

A full sleep cycle averages around 90 minutes, moving through light, deep and REM sleep. Waking at the end of a cycle usually feels far less groggy than waking mid-cycle.

How many cycles do I need?

Most adults do well on 5–6 cycles, which is 7.5–9 hours. Four cycles (6 hours) works short-term but is not sustainable for most people.

❓ More Questions

Why 90 minutes?

A full sleep cycle averages about 90 minutes, moving through light sleep, deep sleep, and REM. Waking at the end of a cycle is usually far fresher than being jolted awake during deep sleep.

How many cycles per night?

Most adults do well with 5-6 cycles (7.5-9 hours). Four cycles (6 hours) works short term but builds sleep debt over time.

💡 Use Cases

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Early Meeting

Set a bedtime that avoids grogginess.

✈️

Jet Lag

Rebuild a sleep schedule.

📚

Study Nights

Choose the least damaging short sleep.

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📖 Deep Dive: Sleep Calculator

What is a sleep cycle

Human sleep is not uniform; it cycles through N1 light, N2, N3 deep, and REM rapid-eye-movement stages, with one full cycle averaging about 90 minutes. A night usually has 4-6 cycles.

Why waking at cycle end feels better

If the alarm rings during deep sleep (N3), the brain needs a long time to wake up; this grogginess, called sleep inertia, can last 15-30 minutes or more. Waking near the end of a cycle, close to light sleep, is far more natural.

How it is calculated

This tool steps 90 minutes forward or backward from your target time and adds about 15 minutes to fall asleep (the average time from lying down to sleeping for most people).

Practical tips for better sleep

A fixed schedule matters more than total hours.

Avoid bright light and screen blue light one hour before bed.

Caffeine has a half-life of about 5-6 hours; avoid it after noon.

Bedroom temperature of 18-22 C is usually best for falling asleep.

Reminder

90 minutes is a population average; individual cycles range 70-110 minutes. This tool is for reference; for chronic insomnia or sleep apnea, see a doctor.