MedlinePlus
medlineplus.gov
Plain-language health information from the US National Library of Medicine
No sign-up
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sleepfoundation.org
Explains sleep with a medical review panel, plus bedtime and cycle calculators.
Long-form guides on insomnia, apnoea, shift work, children's sleep and the rest, each with a named medical reviewer and citations to the research it summarises — which is what separates it from the enormous amount of sleep content that cites nothing. The bedtime calculator works backwards from your wake time in ninety-minute cycles. Treat it as orientation before a doctor's appointment rather than an answer.
AltFTool does this too
If you would rather not leave the site, Sleep Calculator covers the same job here — free, no account, and it runs in your browser.
Open Sleep CalculatorQuestions
Works the moment the page loads. No account, no email, no trial. It is general education, not medical advice — persistent sleep problems need a clinician, and the site funds itself partly through mattress reviews.
Yes. Sleep Foundation sends your input to its own servers to process it. That is fine for public material; for anything containing personal data, use one of the on-device tools instead.
It is general education, not medical advice — persistent sleep problems need a clinician, and the site funds itself partly through mattress reviews.
Alternatives
Same category or same task, ordered by how closely they overlap.
medlineplus.gov
Plain-language health information from the US National Library of Medicine
omnicalculator.com
Around 3,000 small calculators, each with the formula shown underneath
drugs.com
Lists the interactions between the medicines, supplements and alcohol you enter
exrx.net
An exercise library that names the muscles each movement actually works
fdc.nal.usda.gov
The USDA's laboratory-measured nutrient data for tens of thousands of foods
kingarthurbaking.com
Gives the gram weight of a cup of every baking ingredient you are likely to use