How to Use the Calorie Calculator
This calculator estimates your Basal Metabolic Rate (BMR) using the Mifflin-St Jeor equation, scales it up to Total Daily Energy Expenditure (TDEE) with an activity multiplier, applies a calorie adjustment for your goal, and splits the resulting target into protein, carbohydrate, and fat grams. These are evidence-based starting points — individual variation means real needs may be 10-15% higher or lower.
How the math works
- BMR (Basal Metabolic Rate): calories your body burns at complete rest. The Mifflin-St Jeor equation is: men, BMR = 10 x weight(kg) + 6.25 x height(cm) - 5 x age + 5; women, BMR = 10 x weight(kg) + 6.25 x height(cm) - 5 x age - 161. It is the most accurate general-population equation currently recommended by the Academy of Nutrition and Dietetics.
- TDEE (Total Daily Energy Expenditure): BMR x activity multiplier. Sedentary desk workers use about 1.2x; light exercise 1-3 days/week uses 1.375x; moderate exercise 3-5 days/week uses 1.55x; heavy training 6-7 days/week uses 1.725x; and athletes with very hard daily training use up to 1.9x.
- Calorie target: a 500 kcal/day deficit or surplus changes body weight by roughly 1 lb/week, since a pound of body fat stores about 3,500 kcal. This calculator applies that adjustment directly to TDEE based on your selected goal.
- Macronutrients: the target calories are split roughly 30% protein, 40% carbohydrate, and 30% fat, then converted to grams using 4 kcal/g for protein and carbs and 9 kcal/g for fat. Protein needs (0.7-1g per lb of body weight) can be adjusted higher for strength training or weight loss.
Common calibration mistakes
- Overestimating activity level — most people select "moderately active" when their true TDEE puts them in the sedentary-to-lightly-active range.
- Tracking calories burned from exercise and adding them back to your target — the activity multiplier already accounts for typical exercise. Double-counting creates an unintended surplus.
- Chasing an aggressive deficit. Going far below 1,200-1,500 kcal/day without medical supervision risks nutrient deficiency and muscle loss — treat the output as a starting point and adjust every 2-3 weeks based on observed weight trend.
This calculator provides educational estimates for healthy adults and is not a substitute for professional medical or nutritional advice. Consult a doctor or registered dietitian before making significant changes to your diet, especially if pregnant, breastfeeding, or managing a medical condition.
Frequently Asked Questions
What formula does this calculator use?
It uses the Mifflin-St Jeor equation to estimate Basal Metabolic Rate (BMR): for men, BMR = 10 x weight(kg) + 6.25 x height(cm) - 5 x age + 5; for women, BMR = 10 x weight(kg) + 6.25 x height(cm) - 5 x age - 161. BMR is then multiplied by an activity factor (1.2 to 1.9) to estimate Total Daily Energy Expenditure (TDEE).
How many calories should I eat to lose weight?
A deficit of about 500 calories per day below your TDEE corresponds to roughly 1 pound of fat loss per week, since one pound of body fat is approximately 3,500 calories. A 250-calorie daily deficit produces about half a pound of loss per week. Avoid deficits below 1,200-1,500 calories/day without medical supervision.
How is the protein, carb, and fat breakdown calculated?
This calculator splits your daily calorie target roughly 30% protein, 40% carbohydrate, and 30% fat, then converts each share to grams using 4 calories per gram of protein and carbohydrate and 9 calories per gram of fat. Individual needs vary, especially for athletes or specific medical diets.
Is this calculator a substitute for medical advice?
No. These are population-level estimates for healthy adults. Pregnancy, breastfeeding, chronic illness, eating disorders, and certain medications can change energy needs significantly, so consult a doctor or registered dietitian before making major changes to your diet.