SleepWakeCalc is a free sleep cycle calculator built around a single idea: most other sleep calculators tell you a list of times without ever showing you what is actually happening across the night. Ours does. The interactive timeline displays the four sleep stages — light (N1, N2), deep (N3), and REM — across each 90-minute cycle, so you can see why one bedtime works and another doesn't.
Methodology
The calculator is built on three published assumptions that are openly adjustable in the interface:
- Cycle length defaults to 90 minutes, the population mean for healthy adults reported across decades of polysomnography research. Adjustable from 70 to 110 minutes via the settings panel to match individual variation.
- Sleep latency defaults to 15 minutes, the population mean for the time between getting into bed and falling asleep in healthy adults without insomnia. Adjustable from 0 to 45 minutes.
- Recommended cycle counts are age-stratified using the consensus sleep duration recommendations of the National Sleep Foundation and CDC: 5–6 cycles for adults, 5–7 for teens, 6–8 for school-age children, 7–8 for preschoolers, 7–9 for toddlers, and 5 for seniors.
The visual sleep stage proportions in the timeline reflect the average distribution of N1, N2, N3, and REM across consecutive cycles in a healthy adult night, with deep sleep loaded into the early cycles and REM into the later ones — a well-documented pattern in sleep medicine.
Sources we cite
Our articles and recommendations are drawn from these published bodies of work:
- Centers for Disease Control and Prevention — Sleep and Sleep Disorders.
- National Sleep Foundation — Sleep Duration Recommendations.
- American Academy of Sleep Medicine — clinical practice guidelines and the AASM Manual for the Scoring of Sleep.
- Peer-reviewed sleep research published in Sleep, Journal of Clinical Sleep Medicine, and Sleep Medicine Reviews.
- American Academy of Pediatrics — adolescent sleep recommendations.
When our articles make a specific claim about sleep biology, we link to the underlying source. We do not generate medical advice with AI and we do not invent citations.
Who we are
SleepWakeCalc is built and maintained by an independent team of web engineers and editors. We are not a clinic. We do not diagnose, treat, or prescribe. We do not have a financial relationship with any sleep-product company we link to. If we eventually recommend a product through an affiliate link, we will disclose it clearly on that page.
What this site is not
This is not a substitute for a sleep clinician. If you have chronic insomnia, suspected sleep apnea, restless legs, persistent daytime fatigue despite adequate sleep duration, or any sleep symptom that has lasted more than four weeks, the right next step is a conversation with a primary-care doctor. A sleep cycle calculator helps you optimize a baseline. It cannot replace a diagnosis.
How the site is funded
The site is free and runs on display advertising. We use Google AdSense and may eventually move to Ezoic or Mediavine when traffic grows. Ads are placed in fixed positions you can identify, never in misleading layouts, and never inside the calculator interface itself. You can read more about our advertising practices in our privacy policy.
Updates and corrections
We update articles and the calculator when:
- The CDC or AASM publishes new guidance
- A reader points out an error (we are grateful — please do)
- New research changes the consensus on a specific number
Each article shows its publish date and last-reviewed date. If you find an error, contact us and we will fix it.
Contact
For feedback, corrections, partnership inquiries, or to report a bug: contact page.