These tools chain together. The energy chain starts with the BMR calculator (what your body burns at rest, via the Mifflin-St Jeor equation), scales through the calorie calculator (your real daily burn and goal targets), and ends at the macro calculator (how to split those calories between protein, carbs and fat). The body-composition chain pairs the famous-but-limited BMI with the more honest body fat percentage and the formula-skeptical ideal weight tool.

For training, the running pace calculator converts speeds and predicts race times via Riegel's formula, while the heart rate zones tool maps effort — including the Karvonen method. Daily-life tools round it out: water intake (myth-checked), sleep cycles (bedtime arithmetic that respects 90-minute cycles), and the pregnancy due date calculator with honest accuracy framing.

Every formula is named and cited on its page, with its error bars stated rather than hidden — these are screening estimates, not diagnoses, and your clinician outranks every calculator here. Background reading lives in the blog, starting with how many calories you actually need.