About HydrateCheck

HydrateCheck is the water math: how much you actually need, what a workout costs in fluid, your personal sweat rate, and when the last coffee should happen.

HydrateCheck exists because hydration advice is either folklore (8 glasses) or sports-lab complexity. The middle — body-weight-based baselines, sweat-rate tests you can run yourself — is what these calculators provide.

Every calculator on HydrateCheck shows its formula and its assumptions on the page, so you can check the math, reproduce it in a spreadsheet, or argue with it. Inputs are processed entirely in your browser — nothing is sent to a server, and there are no accounts.

HydrateCheck is an independent, ad-supported project. We are not affiliated with any lender, brand, agency, or the sources we cite (NIH and CDC public guidance). If a number looks wrong, the contact page reaches a human who fixes it.

What makes HydrateCheck different

• Your numbers never leave your browser. Every calculator on HydrateCheck runs entirely on your device. We never see, store, or transmit the figures you enter — there are no accounts and no server-side processing of your inputs.
• Published methodology. Each calculator page explains the exact formula it uses and the assumptions behind it, so you can check our work or reproduce it in a spreadsheet.
• Free, forever, without a paywall. HydrateCheck is supported by advertising. There is no premium tier, no email gate, and no upsell.

Independence

HydrateCheck is an independent educational project. We are not affiliated with, endorsed by, or acting on behalf of any government agency, lender, insurer, or the organizations whose formulas and public data we reference (such as NIH and CDC public guidance). All trademarks and referenced standards belong to their respective owners.

Questions, corrections, or suggestions are genuinely welcome — get in touch.