How BMI is calculated
Body Mass Index divides weight by the square of height, giving a simple screening number used widely because it only needs two measurements.
BMI categories: under 18.5 is underweight, 18.5–24.9 is normal weight, 25–29.9 is overweight, and 30 or above is classified as obese. BMI doesn't distinguish muscle from fat, so it can be misleading for very muscular individuals.
How BMR and TDEE are calculated
Basal Metabolic Rate (BMR) is the calories your body burns at complete rest, just to keep basic functions running. This tool uses the Mifflin-St Jeor equation, widely considered one of the more accurate formulas for the general population:
TDEE (Total Daily Energy Expenditure) multiplies BMR by an activity factor to estimate total calories burned per day, including movement and exercise — this is your maintenance calorie level.
Using TDEE for a goal
To maintain weight, eat around your TDEE. A common approach for weight loss is a modest deficit (roughly 300-500 calories below TDEE), and for weight gain, a similar surplus — always alongside professional guidance for anything beyond general awareness.
Frequently asked questions
Is BMI accurate for everyone?
BMI is a population-level screening tool, not a diagnosis. It doesn't account for muscle mass, bone density, or body composition, so it can misclassify very muscular or very lean individuals. Use it as one data point, not the whole picture.
Is this medical advice?
No — this tool provides general estimates for informational purposes only. For personalized nutrition or health guidance, consult a doctor, dietitian, or other qualified professional.