About SleepCalculator
SleepCalculator is a set of free tools for timing sleep. You give a time, you get times back. No account, no email, no tracking, and nothing to buy.
How the calculators work
Sleep runs in cycles averaging about 90 minutes. Every tool on this site counts those cycles forward from a bedtime or backward from an alarm, and adds roughly 15 minutes for the time it takes to fall asleep. The arithmetic is deliberately simple and it is all visible: no model, no personalisation, nothing hidden behind a score.
Where a tool uses a different formula, it says so. Sleep efficiency is time asleep over time in bed. REM estimates weight the later cycles more heavily, because that is where REM actually sits. Age recommendations come from published consensus ranges rather than from our own opinion.
Editorial standards
Content is written and maintained by SleepCalculator Editorial Team. Every page carries a byline and a last-checked date, and links to the primary sources it draws on.
We are not clinicians, and we do not present ourselves as any. What you get here is careful reading of the published literature, stated plainly, with the uncertainty left in rather than smoothed over. Where the evidence is thin, the pages say so; where a popular claim does not hold up, they say that too.
No medical professional currently reviews this content. We would rather state that than imply a review that has not happened. If you are a sleep clinician willing to review these pages, get in touch.
How pages are written
- Every factual claim traces to a public, citable source. Sources are linked on the page, not buried.
- Where guidance is contested or the evidence is weak, the page says which, instead of picking a side quietly.
- Pages carry a last-checked date. It moves when the content is actually reviewed, not on every deploy.
- Corrections are made in place, and we would rather hear about an error than not.
- No affiliate links inside the guidance. Anything commercial sits in the footer and is labelled.
Our sources
A note on medical advice
SleepCalculator is for scheduling and general information. It is not a diagnosis, a treatment, or a substitute for professional care. Persistent trouble falling or staying asleep, loud snoring with pauses in breathing, or daytime exhaustion despite adequate time in bed are all signs of conditions a doctor can treat. Insomnia, sleep apnea and circadian rhythm disorders are common and treatable, and no calculator will fix them.
Contact
Corrections, questions, or a spotted error: [email protected], or use the contact page. We read everything.