How the numbers are built
This starts with your BMR — the energy your body needs at total rest — then multiplies it by an activity factor matching how much you move in an average week. The result is your maintenance calories. Subtracting roughly 250–500 kcal targets gradual fat loss; adding the same amount targets gradual weight gain.
A worked example
A 30-year-old man at 75 kg and 175 cm, moderately active, has a BMR of about 1,699 kcal and maintenance calories of roughly 2,633 kcal/day. Targeting steady weight loss would put daily intake closer to 2,133 kcal, while steady weight gain would mean closer to 3,133 kcal.
Frequently asked questions
What is BMR and how is it different from TDEE?
BMR (Basal Metabolic Rate) is roughly how many calories your body burns at complete rest just keeping organs running. TDEE (Total Daily Energy Expenditure) takes BMR and multiplies it by an activity factor to account for movement, exercise and daily life — TDEE is the number that actually represents your maintenance calories.
Why does this use the Mifflin-St Jeor equation specifically?
Mifflin-St Jeor (1990) is generally considered more accurate for most modern adults than older formulas like Harris-Benedict, which was developed from a narrower population over a century ago. It's the equation most commonly recommended by dietitians today.
How big a calorie deficit should I actually aim for?
A deficit of about 500 kcal/day tends to produce roughly 0.5 kg (about 1 lb) of weight loss per week, since roughly 7,700 kcal corresponds to 1 kg of body fat. Larger deficits speed this up but become harder to sustain and can affect energy levels and muscle retention.
Why might my real-world results differ from this number?
This is an estimate based on population averages — individual metabolism, muscle mass, sleep, stress and even genetics shift the real number up or down. Treat it as a starting point, then adjust based on how your actual weight trends over 2-3 weeks.
This calculator provides general estimates only and is not medical or nutritional advice. Consult a doctor or registered dietitian before making significant changes to your diet.