Why I built this

Last updated: 6 August 2026

I'm a product manager in IT with an undergraduate degree in math and a master's in international finance. So I feel comfortable around dashboards and formulas.

Hydration advice online is mostly folklore repeated with confidence. Eight glasses a day, coffee doesn't count, drink until your urine is clear. The calculators I came across either hid their formula or made one up. I wanted the formulas present, the assumptions transparent, and the sources cited. That's what I've tried to build here.

I'm not a doctor, a dietitian, or an exercise physiologist. I'm a guy on the internet who did the research and built some calculators. I run a handful of niche calculator sites in my spare time because I enjoy the work. Every assumption is shown, every number has a source linked. You change the inputs, you make the call.

Editorial principles

Every calculator is built on published guidance or peer-reviewed research: IOM, EFSA, ACSM, ISSN, WHO, NPS, CDC. Sources are named on the page that uses them.
Where the evidence gives a range, the result is a range. Sweat sodium runs from roughly 400 to 1,600 mg per litre between people, so the calculator says so instead of inventing a single number.
The calculators do not diagnose anything. Every page carries a "not medical advice" line, and the conditions and medicines that change the answer are named where they matter.
All calculations run in your browser. No data leaves your device, and no account is required.
When a number here turns out to be wrong, it gets changed and the change is visible. The rehydration mix on this site once carried weaker figures than the WHO formula it named; that has been corrected.

How I use AI

HydrationGuide is drafted with AI assistance and reviewed by hand before anything goes live. I use AI the way a working writer uses a research assistant: it speeds up the labor, it does not replace the judgment. The methodology page sets out exactly what that does and does not cover.

Who is behind it

HydrationGuide is run by Reede Taylor, independently, from the Netherlands. It is not a company or a clinic, it has no staff, and it has no relationship with any supplement or drinks manufacturer. Nothing on the site is sponsored.

Every formula and its sources live on the methodology page. If you spot something wrong, tell me. I fix things when the data changes.

— Reede

These tools are for informational purposes only and not a substitute for medical advice. For health concerns, talk to a healthcare provider.