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From your body to a daily calorie target

This calculator answers two linked questions: how many calories does your body burn in a day, and how should those calories be split between protein, fat, and carbohydrate to support a goal? It does this with the same equations dietitians and sports scientists use, so the numbers are grounded rather than guessed. You enter your gender, age, height, weight, and activity level; it returns your BMR, your TDEE, and a goal-by-goal table of calorie and macronutrient targets.

BMR and TDEE, explained

Your Basal Metabolic Rate (BMR) is the energy your body uses at complete rest just to stay alive — heartbeat, breathing, brain, temperature. This tool uses the Mifflin-St Jeor equation, the most accurate general-population formula in current use:

• Men: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5
• Women: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age − 161

Your Total Daily Energy Expenditure (TDEE) is BMR multiplied by an activity factor, because moving burns more than resting:

TDEE is your maintenance level — eat that, and your weight stays roughly stable.

A worked example

Take a 30-year-old man, 170 cm, 70 kg, lightly active. BMR = 10 × 70 + 6.25 × 170 − 5 × 30 + 5 = 700 + 1062.5 − 150 + 5 = 1617.5, which rounds to 1,618 kcal. Multiply by the 1.375 light-activity factor: TDEE ≈ 2,224 kcal. That is his maintenance. The goal table then offsets it: moderate loss subtracts 250 (≈1,974 kcal), weight loss subtracts 500 (≈1,724 kcal), gain adds the same amounts. A 500-kcal daily deficit corresponds to roughly half a kilogram of fat per week, the widely cited safe rate.

How the macros are split

For every goal row, the tool divides the calories into three macronutrients using a fixed, sensible rule:

• Protein is fixed at 2 g per kg of body weight (so 140 g for our 70 kg example), worth 4 kcal per gram. Setting protein by body weight rather than a percentage is the modern approach — it protects muscle in a deficit and supports growth in a surplus.
• Fat is set to 25% of total calories, at 9 kcal per gram, the most energy-dense macronutrient.
• Carbohydrate fills whatever calories remain, at 4 kcal per gram — your main training fuel.

Because protein is pegged to your weight rather than your calories, its percentage rises automatically as you cut calories, which is exactly what you want when losing weight.

Practical tips

• Be honest about activity. Over-estimating your activity level is the most common reason a deficit stalls — most desk workers who exercise a few times a week are "lightly" or "moderately" active, not "very active."
• Pick a goal you can sustain. The aggressive 500-kcal deficit works, but the 250-kcal "moderate" option is easier to hold for months and preserves more muscle and energy.
• Recalculate as your weight changes. Both BMR and the 2 g/kg protein target depend on current body weight, so update your inputs every few kilograms.
• Switch units freely. Toggle between metric and imperial; the tool converts feet/inches and pounds to centimetres and kilograms internally before applying the formula, so the result is identical either way.

Common mistakes and important limits

• Treating the number as exact. Mifflin-St Jeor is a population average; real metabolism varies by ±10% or more between individuals. Use the figure as a starting point, then adjust based on three to four weeks of real-world weight change.
• Ignoring food quality. Hitting your macros with mostly ultra-processed food still leaves you short on fibre and micronutrients. Macros are a budget, not a meal plan.
• Eating too little. Dropping far below your BMR is counterproductive and unsustainable. The deficit options here cap at 500 kcal for good reason.

This is an educational estimate, not medical advice. The calculation runs entirely in your browser — nothing you enter is uploaded. If you have a health condition, are pregnant, or have a history of disordered eating, consult a doctor or registered dietitian before changing your intake.