BMI Calculator
Calculate your Body Mass Index, BMI category, and daily calorie needs (BMR/TDEE).
About the BMI Calculator
Body Mass Index is your weight in kilograms divided by the square of your height in meters: BMI = weight (kg) / height (m)². The result places you into one of four WHO categories — underweight (under 18.5), normal weight (18.5–24.9), overweight (25–29.9), or obese (30+). This calculator also estimates your Basal Metabolic Rate (BMR) using the Mifflin-St Jeor equation, which for men is 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5 and for women is the same minus 161 instead of plus 5. Multiplying BMR by an activity multiplier (roughly 1.2 for sedentary up to 1.9 for very active) gives your Total Daily Energy Expenditure (TDEE) — an estimate of the calories you burn in an average day including exercise.
To use it: enter your sex, age, height in centimeters, weight in kilograms, and typical activity level, and every result updates immediately. For example, a 30-year-old male at 175 cm and 75 kg has a BMI of 75 / 1.75² ≈ 24.5 (normal weight), a BMR of roughly 10×75 + 6.25×175 − 5×30 + 5 ≈ 1,724 kcal/day, and at moderate activity (×1.55) a TDEE of about 2,672 kcal/day. Use TDEE as a starting point for a calorie target: eating below it tends to produce weight loss and above it weight gain, adjusted to your goals.
What is BMR and TDEE?+−
BMR (Basal Metabolic Rate) is the calories your body burns at rest. TDEE (Total Daily Energy Expenditure) multiplies BMR by your activity level to estimate total daily calorie needs.
Is BMI a perfect health measure?+−
No — BMI doesn't distinguish muscle from fat, so it can misclassify very muscular or very lean people. It's a useful population-level screening tool, not a diagnosis.
What BMI ranges count as underweight, normal, overweight, or obese?+−
Under 18.5 is underweight, 18.5–24.9 is normal weight, 25–29.9 is overweight, and 30 and above is obese, per the WHO adult classification used by this calculator.
Why does the calculator ask for age and activity level if BMI only needs height and weight?+−
BMI itself only needs height and weight. Age and activity level feed the separate BMR/TDEE estimate — the Mifflin-St Jeor equation includes age because metabolism slows with it, and activity level scales BMR up to account for exercise.
How accurate is the Mifflin-St Jeor BMR formula?+−
It's generally considered one of the more accurate BMR predictors for the general population, typically within about 10% of measured resting metabolic rate, though individual variation (muscle mass, genetics, medical conditions) can push actual values outside that range.
Should I eat exactly at my TDEE?+−
TDEE is your estimated maintenance calorie level. Eating below it over time tends to produce weight loss, eating above it tends to produce weight gain, and eating at it tends to maintain your current weight — treat it as a starting point to adjust from, not a precise prescription.
Does this calculator store my height, weight, or age anywhere?+−
No — every field is held only in your browser's memory for the current session and is recalculated locally. Nothing is sent to a server or saved once you close the tab.