Macronutrient Calculator (Protein / Carbs / Fat)

Given a daily calorie target, split it into protein / carb / fat grams using preset ratios or custom sliders. Math is simple: protein and carbs are 4 kcal/g, fat is 9 kcal/g. Presets cover the four most common approaches: balanced (30/40/30), low-carb (35/25/40), high-protein (40/35/25), and keto (25/5/70). Shows grams, kcal, and grams-per-kg-bodyweight for each macro — useful for hitting protein targets like 1.6-2.2 g/kg for muscle gain.

The 4/4/9 figures are Atwater factors, a nineteenth-century average that food labels still use. They are close enough for planning and wrong in the details: fibre is counted as carbohydrate here but yields little or nothing, which is why some approaches track net carbs instead, and alcohol is about 7 kcal/g and appears in none of the three columns. A day with a couple of drinks in it does not add up.

The split is arithmetic on a number you supplied, so everything rests on that calorie target being right. Estimates from height, weight and activity are population averages, and individual expenditure varies by several hundred kilocalories around them. The honest way to find yours is to hold an intake steady for a fortnight and watch the trend on the scale, then adjust; no formula shortcuts that.

Protein is the one macro with a floor worth respecting. The grams-per-kilogram figure is there because the useful range is defined that way rather than as a share of calories: at a low calorie target a 40% protein split can land below 1.6 g/kg while looking high, and the percentage hides it. For anyone carrying a lot of fat mass, the usual advice is to compute the target against a lean or goal bodyweight rather than current weight.

These are planning numbers, not medical advice. Anyone with kidney disease, diabetes or an eating disorder history should be working from a clinician's figures rather than a slider.