Learn how to calculate your daily calorie needs using the Mifflin-St Jeor equation and TDEE. Covers calorie goals for weight loss, maintenance, and muscle gain with examples.
Calories are the fundamental currency of body weight. Eat more than you burn and you gain weight. Eat less and you lose it. The challenge is knowing exactly how many calories your body burns — and that number is far more personal than most people realize. A sedentary 45-year-old woman and an active 25-year-old man might have daily calorie needs that differ by 1,200 calories or more. Getting your number right is the starting point for any meaningful nutrition plan.
Your BMR is the number of calories your body burns at complete rest just to maintain basic functions — breathing, circulation, temperature regulation, organ function. It typically accounts for 60–70% of your total daily calorie burn.
The Mifflin-St Jeor equation is the most accurate validated formula for most adults, according to the American Journal of Clinical Nutrition:
Men: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) + 5
Women: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) − 161
Since you're not lying still all day, multiply your BMR by an activity factor to get your TDEE — the actual total calories you burn daily:
| Activity Level | Multiplier | Description |
|---|---|---|
| Sedentary | × 1.2 | Desk job, little or no exercise |
| Lightly active | × 1.375 | Light exercise 1–3 days/week |
| Moderately active | × 1.55 | Moderate exercise 3–5 days/week |
| Very active | × 1.725 | Hard exercise 6–7 days/week |
| Extra active | × 1.9 | Physical job + hard training daily |
Example continued: Our 32-year-old woman, moderately active:
TDEE = 1,360 × 1.55 = 2,108 calories/day to maintain current weight
A calorie deficit of 500 calories/day typically produces ~0.5 kg (1 lb) of weight loss per week — a rate most people can sustain without losing significant muscle.
Weight loss target: TDEE − 500 = 2,108 − 500 = 1,608 calories/day
Do not go below 1,200 calories/day (women) or 1,500 calories/day (men) without medical supervision. Extreme deficits cause muscle loss, nutrient deficiencies, and metabolic adaptation.
Eat at TDEE: 2,108 calories/day
A calorie surplus of 200–300 calories above TDEE minimizes fat gain while supporting muscle building:
Muscle gain target: TDEE + 250 = 2,108 + 250 = 2,358 calories/day
The commonly cited "1 pound of fat = 3,500 calories" is a useful approximation, but not perfectly accurate. Over short periods, weight loss comes from a mixture of fat, water, and muscle — not pure fat. Early in a diet, the deficit needed per pound of weight lost is often less than 3,500 calories because some of the lost mass is water. Over longer periods, the body adapts, and the deficit required per pound increases as metabolic rate slows.
This metabolic adaptation means that as you lose weight, you need to recalculate your TDEE periodically — your calorie needs decrease as your body gets lighter.
The three macronutrients provide the bulk of your calories:
TDEE estimates have significant individual variation. Studies show that real-world calorie needs can differ by 15–20% from calculations based on the same formula. Factors include muscle mass (more muscle = higher BMR), non-exercise activity thermogenesis (NEAT — fidgeting, posture, general movement), gut microbiome differences affecting caloric extraction from food, and genetics.
The only reliable way to know your real TDEE: Eat a consistent number of calories for 2–3 weeks and track your weight. If weight is stable, that's your maintenance. Adjust from there.
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