Calorie Calculator

Understanding how many calories your body needs each day is the foundation of any nutrition plan, whether the goal is weight loss, muscle gain, or simply maintaining your current physique. This free calorie calculator uses the Mifflin-St Jeor equation, which is widely regarded by nutrition researchers as the most accurate predictive formula for estimating resting metabolic rate in healthy adults.

The calculator works in two steps. First, it determines your Basal Metabolic Rate (BMR) -- the number of calories your body burns at complete rest just to keep vital functions running: breathing, circulating blood, growing cells, and regulating body temperature. BMR typically accounts for 60 to 75 percent of your total daily energy expenditure. Second, it applies an activity multiplier to your BMR to estimate your Total Daily Energy Expenditure (TDEE), which represents the actual number of calories you burn in a typical day when accounting for exercise and daily movement.

The Mifflin-St Jeor equation was published in 1990 and has since been validated in numerous clinical studies. For men, the formula is: BMR = 10 * weight(kg) + 6.25 * height(cm) - 5 * age + 5. For women, the formula is: BMR = 10 * weight(kg) + 6.25 * height(cm) - 5 * age - 161. These formulas were derived from indirect calorimetry measurements of hundreds of subjects and have been shown to predict measured resting metabolic rate within 10% for most individuals.

Once you have your TDEE, the calculator adjusts for your specific goal. For weight loss, it subtracts 500 calories per day from your TDEE, which creates a weekly deficit of approximately 3,500 calories -- roughly equivalent to one pound of fat loss per week. For weight gain, it adds 500 calories per day to support lean mass growth. The maintenance option leaves your TDEE unchanged. These adjustments are general guidelines, not rigid prescriptions. Individual results vary based on body composition, hormonal factors, sleep quality, and metabolic adaptation.

The macro breakdown provides a starting point for structuring your diet. The default split is 30% protein, 40% carbohydrates, and 30% fat, which aligns with mainstream sports nutrition recommendations. Protein is set at 30% to support muscle maintenance during calorie restriction and muscle growth during surplus phases. Each gram of protein contains 4 calories, each gram of carbohydrate contains 4 calories, and each gram of fat contains 9 calories. The calculator converts your calorie targets into grams for each macronutrient so you can plan meals accordingly.

Keep in mind that calorie calculators provide estimates, not guarantees. Factors like genetics, gut microbiome composition, medication use, stress levels, and sleep patterns all influence real-world energy balance. Use this tool as a starting reference, then adjust based on how your body responds over two to four weeks. If you have specific medical conditions or dietary requirements, consult a registered dietitian or healthcare provider for personalized guidance.

This calculator uses the Mifflin-St Jeor equation (1990), which has been validated as the most accurate non-laboratory method for estimating resting metabolic rate. Activity multipliers follow the standard Harris-Benedict activity factors: Sedentary (1.2), Lightly Active (1.375), Moderately Active (1.55), Active (1.725), and Very Active (1.9). Goal adjustments use the commonly recommended 500 calorie per day surplus or deficit. Macro percentages follow the 30/40/30 protein/carbs/fat split. All calculations run entirely in your browser -- no personal data is transmitted or stored.