Macronutrient Calculator
Work out your daily protein, carb and fat grams from your TDEE, goal and chosen macro split.
- BMR (Mifflin-St Jeor)
- — kcal
- TDEE (maintenance)
- — kcal
- Daily calorie target
- — kcal
Protein
— g / day
—% · — kcal · — g per meal
Carbs
— g / day
—% · — kcal · — g per meal
Fat
— g / day
—% · — kcal · — g per meal
Heads up: this target is under 1,200 kcal a day. Very low intakes are hard to hit nutritionally and should only be done with professional supervision.
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These numbers are estimates from population-average equations, not medical advice. Real energy needs vary by 10–20% between people of the same size, and medical conditions, pregnancy, breastfeeding and medication change them further. Talk to a doctor or a registered dietitian before making big changes to what you eat.
How it works
The calculator starts from the Mifflin-St Jeor equation, the resting-metabolism
formula most dietitians use today: BMR = 10 × kg + 6.25 × cm − 5 × age + 5 for men
and … − 161 for women. Multiplying your BMR by an activity factor (1.2 sedentary up
to 1.9 extra active) gives your TDEE — the calories you burn in a normal day. Your goal then
shifts that by up to 20% either way to produce a daily calorie target.
That target is divided across the three macronutrients using the split you pick, then converted to grams with the Atwater factors: protein and carbohydrate supply 4 kcal per gram and fat 9 kcal per gram. Pick a preset — balanced, high protein, low carb, endurance or keto — or choose “Custom…” and enter your own percentages (they must add up to 100). Everything recalculates as you type, and the per-meal column divides the day by the number of meals you eat. All of the arithmetic runs in your browser in plain JavaScript: nothing about your body is uploaded, stored or sent anywhere, and there are no ads or sign-ups.
Frequently asked questions
How does the macro calculator work out my numbers?
It runs three steps. First it estimates your resting metabolic rate with the Mifflin-St Jeor equation — BMR = 10 × weight in kg + 6.25 × height in cm − 5 × age + 5 for men, and the same expression minus 161 for women — the equation the Academy of Nutrition and Dietetics recommends for healthy adults. Second it multiplies that BMR by an activity factor from 1.2 (sedentary) to 1.9 (extra active) to get your TDEE, the calories you burn on an average day, then shifts it by up to 20% up or down for your goal. Third it splits that calorie target across the macros using the percentages you pick and converts each slice to grams with the Atwater factors: 4 kcal per gram of protein, 4 per gram of carbohydrate and 9 per gram of fat.
What macro split should I use?
There is no single right answer, which is why the tool offers presets and a custom option. A balanced 30% protein / 40% carbs / 30% fat suits most people who just want a sensible target. High protein (40/40/20) suits anyone in a calorie deficit who wants to hold on to muscle, since protein is the most filling macro and the most protective of lean mass. Low carb (40/20/40) and keto (25/5/70) suit people who prefer fat as their main fuel — keto pushes carbs low enough to reach ketosis. Endurance athletes usually want the opposite, around 25/55/20, because carbohydrate is the fuel that limits long hard sessions. Pick the one that matches how you actually like to eat: adherence beats optimisation.
How accurate are these macro targets?
Treat them as a well-informed starting point, not a measurement. Mifflin-St Jeor predicts measured resting metabolic rate within about 10% for roughly four out of five healthy adults, so two people with identical height, weight, age and sex can genuinely need a few hundred calories a day more or less than each other. Activity multipliers add more scatter, because most people over-estimate how active they are. The practical method is to eat the target consistently for two to three weeks, watch your weight trend, and adjust the calories by about 10% if the trend is not going the way you want. These figures are general information and not medical advice — check with a doctor or a registered dietitian before making significant dietary changes, especially if you are pregnant, breastfeeding, under 18, or managing a medical condition.