Why this Sweat Rate Calculator and Two Numbers on a Bathroom Scale Will Tell You More Than Any Hydration App will. Most triathletes hydrate by feel, or by whatever a bottle-per-hour rule of thumb they picked up years ago. Feel is a bad instrument for this. Thirst lags actual fluid deficit, and by the time it shows up, the workout is already compromised. The fix isn't a smarter app or a fancier bottle — it's two weigh-ins and a little arithmetic.

The Triathlon Fueling Calculator builds a personalized, multi-part race-day nutrition and hydration plan from a short athlete profile. It walks you through your body weight, your race distance, and your realistic finish time, then layers in the conditions and physiology that actually change your numbers.