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Sleep Calculator

Find the best wake-up and bedtime to feel refreshed, based on 90-minute sleep cycles.

Last updated: 2026/10/16 Calculator Feedback & bug reports

I want to wake up at this time

Advanced settings (cycle length & time to fall asleep)

A typical sleep cycle is about 90 minutes, and it usually takes about 15 minutes to fall asleep.

Enter a time and press "Calculate".

How to Use

1

Choose a direction

Pick one of the three tabs: "I want to wake up at", "I go to bed at", or "If I sleep now".

2

Enter a time

Enter your wake-up time or bedtime. No input is needed for "If I sleep now".

3

Check the best times

Press "Calculate" to see candidates aligned to 90-minute cycles. Aim for the times marked "Recommended".

About the Sleep Calculator

Human sleep cycles through light sleep (REM) and deep sleep (non-REM) roughly every 90 minutes. Waking up at the end of a cycle, during light sleep, tends to feel more refreshing than waking up in the middle of deep sleep. This tool uses a 90-minute cycle and the time it takes to fall asleep (about 15 minutes) to calculate the best bedtime and wake-up time. All calculations run entirely in your browser, and your input is never sent to any server.

Features

  • 90-Minute Cycle CalculationInstantly find wake-up times aligned to the end of sleep cycles for a refreshed start.
  • Both Directions + Sleep NowWork backward from a wake time, forward from a bedtime, or calculate for sleeping right now.
  • CustomizableAdjust the cycle length and time to fall asleep to match your own body.
  • Privacy FirstEverything runs in your browser. The times you enter are never sent to a server.

Use Cases

  • Answer "I want to wake at 7am, so when should I go to bed?"
  • Check "If I sleep now, when should I wake up to feel refreshed?"
  • Plan bedtime before early starts: trips, exams, or flights
  • Set a target bedtime for putting children to sleep
  • Reference for the best nap or power-nap length

FAQ

Why calculate with a 90-minute cycle?
Sleep repeats light and deep stages roughly every 90 minutes, and waking at the end of a cycle (during light sleep) tends to feel more refreshing. Cycle length varies by person, so you can change it in the advanced settings.
What is the 15 minutes to fall asleep?
It is an estimate of how long it takes to actually fall asleep after getting into bed. Around 15 minutes is common, and the tool factors this in. You can change it in the advanced settings.
How many cycles should I sleep?
Adults are often recommended 5 to 6 cycles per night (about 7.5 to 9 hours). The tool marks the 5- and 6-cycle options as "Recommended". Required sleep varies from person to person.
Are the times I enter saved?
No. All calculations happen in your browser, and the times you enter are never sent to or stored on any server.
Is this medical advice?
No. This tool offers general guidance based on the concept of sleep cycles and is not a medical diagnosis or advice. If sleep problems persist, please consult a doctor.
Can I use it on my phone?
Yes. It works on smartphones, tablets, and PCs. No installation or sign-up is required.

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Related Guides

90-Minute Sleep Cycles: When to Sleep and Wake Up Refreshed Sleep runs in roughly 90-minute cycles. Learn how REM and non-REM work, how to back-calculate bedtime and wake time, how much sleep you need, and habits to improve quality. Not medical advice.