---
title: "Sleep Cycle Calculator: When to Sleep | Sleepy Platypus"
description: "Find a bedtime for your alarm, or the best time to wake up, counting roughly 90-minute sleep cycles plus time to fall asleep. Free, no sign-up."
url: https://sleepyplatypus.lol/
---

# Sleep cycle calculator

Pick the time your alarm goes off and see when to be in bed, or start from your bedtime and see when to wake. Each option is a whole number of roughly 90-minute cycles, plus the time it takes you to drift off.

## Go to bed at one of these times

To wake up at **7:00 AM**, with lights out at the time shown:

5 cycles: 7 h 30 min asleep, 7 h 45 min with the lights out

11:15 PM lights out 7:00 AM wake up

- Falling asleep (15 min)
- One sleep cycle (90 min)

Real cycles are not all the same length: they differ between people and through the night, so these times are estimates, not a guarantee of waking between cycles.

**Not medical advice.** An estimate for healthy adults. If you often sleep badly or feel sleepy in the day, talk to a doctor.

## How the calculator works

Through the night you move through repeating cycles of lighter sleep, deep sleep and REM (dreaming) sleep. The first REM period usually arrives about 90 minutes after you fall asleep (NINDS). Waking near the end of a cycle, rather than in the middle of deep sleep, tends to feel easier, so the calculator counts back from your alarm in whole cycles and adds the time it takes you to fall asleep.

With the defaults, a 7:00 AM alarm gives lights out at 11:15 PM for five cycles: 15 minutes to drift off, then 7 hours 30 minutes asleep. Choose *Bedtime* to work forwards instead, or press *Now* if you are heading to bed.

## Choosing the settings

**Time to fall asleep:** use what is normal for you. The National Sleep Foundation counts falling asleep within 30 minutes as a sign of good sleep quality in adults. **Cycle length:** 90 minutes is the usual rule of thumb, but in a study of over 6,000 recorded cycles the median was 96 minutes, with wide differences between people (Cajochen et al., 2024). If you often wake groggy, try 95 or 100.

The suggested option is the shortest night that still gives the 7 or more hours the AASM and Sleep Research Society recommend for adults (Watson et al., 2015). Children and teenagers need more: see [sleep needs by age](https://sleepyplatypus.lol/sleep-needs-by-age/).

## Sources

- National Institute of Neurological Disorders and Stroke. [Brain Basics: Understanding Sleep](https://www.ninds.nih.gov/health-information/public-education/brain-basics/brain-basics-understanding-sleep).
- Cajochen C, Reichert C, Münch M, et al. Ultradian sleep cycles: frequency, duration, and associations with individual and environmental factors. *Sleep Health* 2024;10(1 Suppl):S52–S62. [doi:10.1016/j.sleh.2023.09.002](https://doi.org/10.1016/j.sleh.2023.09.002)
- Watson NF, Badr MS, Belenky G, et al. Recommended amount of sleep for a healthy adult: a joint consensus statement of the AASM and Sleep Research Society. *Sleep* 2015;38(6):843–844. [doi:10.5665/sleep.4716](https://doi.org/10.5665/sleep.4716)
- National Sleep Foundation. [What is sleep quality?](https://www.thensf.org/what-is-sleep-quality/) (summarising Ohayon M, et al. *Sleep Health* 2017;3(1):6–19, [doi:10.1016/j.sleh.2016.11.006](https://doi.org/10.1016/j.sleh.2016.11.006)).
- American Academy of Sleep Medicine. [Healthy sleep habits](https://sleepeducation.org/healthy-sleep/healthy-sleep-habits/).

## More sleep tools

Each tool has its own page, works offline once loaded, and links the research behind its numbers.

- [Nap calculator](https://sleepyplatypus.lol/nap-calculator/): When to set the alarm for a 10- or 20-minute power nap or a full-cycle nap.
- [Sleep needs by age](https://sleepyplatypus.lol/sleep-needs-by-age/): How many hours babies, children, teens and adults should sleep, from the AASM and NSF.
- [Sleep debt calculator](https://sleepyplatypus.lol/sleep-debt-calculator/): Add up a week of sleep against your nightly target and see where the hours went.
- [Printable sleep diary](https://sleepyplatypus.lol/sleep-diary/): A two-week diary to print for your doctor, or keep it here and see your averages.

## Recommended

Two free tools from elsewhere for the screen time that happens before bed.

### Keep sleep-app sign-ups out of your inbox

Trying a free sleep sounds app or downloading a bedtime guide that insists on an email address? CleanTempMail gives you a disposable inbox in one click, with no account, and it clears itself after three days.

[Open a temporary inbox](https://cleantempmail.com/)

### Check a sleep-gadget shop before you buy

Found a bargain on blackout blinds or a white-noise machine from a shop you have never heard of? WebTraceCheck's free tools show a domain's registration details and run a website audit before you hand over card details.

[Look up a shop's domain](https://webtracecheck.com/dns-lookup)

## Questions

**Is it better to sleep five cycles or six?**

For most adults, five cycles (about 7.5 hours) or six (about 9) both meet the 7-hour minimum. Four cycles is only 6 hours: an easier wake-up does not make up for the missing sleep.

**Why do I still wake up groggy?**

Your cycles may be longer or shorter than the setting, the time it takes you to fall asleep varies, and an irregular schedule makes waking harder. The AASM advises getting up at the same time every day, weekends included.

**What if I cannot fall asleep?**

If you are still awake after about 20 minutes, the AASM suggests getting up and doing something quiet in dim light until you feel sleepy. If trouble sleeping goes on for weeks, talk to a doctor; a [sleep diary](https://sleepyplatypus.lol/sleep-diary/) helps them see the pattern.