BMI + Calorie Calculator
Body mass index with visual gauge, daily calorie needs (TDEE), macronutrient breakdown, and weight goal planner — all in one. Metric & imperial.
Health information only — not medical advice. BMI, calorie, and macronutrient calculations are estimates based on standard formulas and population averages. Individual metabolic rates vary. These results are not a substitute for personalized advice from a registered dietitian, nutritionist, or healthcare provider. Consult a professional before making significant changes to your diet or exercise routine.
How the calculations work
All calculations run locally in your browser using clinically validated formulas. No data is sent to any server.
⚖️ BMI Formula
BMI = weight(kg) / height(m)². For imperial: BMI = (weight(lbs) × 703) / height(in)². WHO categories: Underweight <18.5, Normal 18.5–24.9, Overweight 25–29.9, Obese ≥30.
🔬 Mifflin-St Jeor BMR
The most accurate widely-used BMR formula. Men: (10 × kg) + (6.25 × cm) − (5 × age) + 5. Women: (10 × kg) + (6.25 × cm) − (5 × age) − 161. More accurate than Harris-Benedict.
🏃 TDEE Activity Multiplier
TDEE = BMR × activity factor. Sedentary 1.2 · Lightly active 1.375 · Moderately active 1.55 · Very active 1.725 · Super active 1.9. Multiplier accounts for daily movement and exercise.
🥗 Macronutrient Split
Macros are calculated from your calorie target. Lose weight: 30% protein / 40% carbs / 30% fat. Maintain: 25% / 50% / 25%. Gain muscle: 30% protein / 50% carbs / 20% fat. Protein and carbs = 4 kcal/g, fat = 9 kcal/g.
🎯 Weight Goal Calculation
3,500 kcal ≈ 1 lb (0.45 kg) of body fat. A 500 kcal/day deficit equals roughly 0.5 kg/week. Enter your target weight and weekly rate, and the calculator shows your required daily calories and estimated timeline.
📏 BMI Limitations
BMI doesn't measure body fat directly. Athletes and highly muscular people often have high BMI despite low body fat. Older adults may have normal BMI with high body fat percentage due to muscle loss (sarcopenia). Use it as a starting guide only.
Mifflin-St Jeor Equation (used in this calculator):
Men: BMR = (10 × weight_kg) + (6.25 × height_cm) − (5 × age) + 5
Women: BMR = (10 × weight_kg) + (6.25 × height_cm) − (5 × age) − 161
TDEE:
TDEE = BMR × Activity Multiplier
Frequently asked questions
What is BMI and how is it calculated?
BMI (Body Mass Index) measures weight relative to height: BMI = kg/m². For imperial units: BMI = (lbs × 703) / (inches²). WHO categories: Underweight (<18.5), Normal (18.5–24.9), Overweight (25–29.9), Obese (≥30). It's a population-level screening tool — not a direct measure of body fat.
What's the difference between BMR and TDEE?
BMR (Basal Metabolic Rate) is the calories your body burns at complete rest to sustain basic functions: breathing, circulation, cell repair. TDEE (Total Daily Energy Expenditure) is your BMR multiplied by an activity factor. TDEE is the number to use when planning your diet — it represents all the calories you actually burn in a day.
How many calories should I eat to lose weight?
A safe calorie deficit is 500 kcal/day below your TDEE, resulting in approximately 0.5 kg (1 lb) of fat loss per week. A 1,000 kcal/day deficit targets ~1 kg/week, but this may not be sustainable. Never go below 1,200 kcal/day (women) or 1,500 kcal/day (men) without medical supervision — extremely low intakes cause muscle loss and nutrient deficiencies.
What macronutrient split should I use?
A standard balanced split is 25–30% protein, 45–55% carbohydrates, and 20–30% fat. For weight loss, higher protein (30–35%) helps preserve muscle during a deficit. For muscle gain, 25–30% protein with 50–55% carbs provides fuel for training. Protein: 4 kcal/g, Carbs: 4 kcal/g, Fat: 9 kcal/g.
Is BMI accurate for athletes and muscular people?
No — BMI can significantly overestimate body fat in people with high muscle mass. Muscle is denser than fat, so an athlete may have a high BMI while having excellent body composition. Similarly, BMI can underestimate body fat in older adults who've lost muscle. Use BMI alongside other metrics like waist circumference, body fat percentage, or a DEXA scan for a complete picture.
Why does this use the Mifflin-St Jeor formula?
The Mifflin-St Jeor equation (1990) has been validated as more accurate than the older Harris-Benedict formula (1919) for predicting resting metabolic rate. Multiple studies show it predicts BMR within ±10% for most adults. The Harris-Benedict formula tends to overestimate BMR by 5–15% for average adults.
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