BMI Calculator – Free Body Mass Index Calculator with Health Analysis
LOADING THINKFORU BMI CALCULATOR...
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WHO & NIH BACKED GUIDELINES
BMI Calculator Body Mass Index Analyzer
Calculate your BMI instantly. Based on World Health Organization standards. Get weight category, ideal weight, calorie needs & personalized health tips.
TDEE = BMR × Activity Factor (1.2 – 1.9)
Harris-Benedict Activity Multiplier — standard in clinical nutrition practice worldwide
Frequently Asked Questions
BMI (Body Mass Index) measures body fatness from height and weight: BMI = kg ÷ m². Developed in the 1830s, it is the standard tool used by the World Health Organization (WHO), CDC, and NIH / NHLBI to classify weight status in adults and children worldwide.
Per the WHO and NIH, a healthy BMI for adults is 18.5 – 24.9. The Harvard T.H. Chan School of Public Health notes Asian populations may face elevated risk starting at BMI 23. Elderly adults often benefit from a slightly higher BMI of 23–28.
BMI cannot distinguish fat from muscle — a known limitation acknowledged by the CDC. Muscular people may show high BMI despite low body fat. Our tool uses the Deurenberg formula (PubMed) which partially adjusts for this. For athletes, DEXA scans provide more accurate body composition data.
Ideal weight range uses the healthy BMI band (18.5–24.9): Min = 18.5 × height(m)², Max = 24.9 × height(m)². This method is endorsed by NIH's clinical obesity guidelines. Our calculator shows this range automatically after entering your details.
TDEE is your total daily calorie burn including activity. We use the Mifflin–St Jeor equation (PubMed, 1990), recognized as one of the most accurate by the Mayo Clinic. Eat at TDEE to maintain weight, 300–500 kcal below to lose fat, or 200–300 kcal above to gain muscle.
BMI ≥ 30 is classified as obese by the WHO and CDC: Class I (30–34.9), Class II (35–39.9), Class III / Morbid (≥ 40). The Mayo Clinic confirms each class carries increasing risk for type 2 diabetes, cardiovascular disease, and sleep apnea.
Yes. For ages 5–17, BMI-for-age percentiles are used. Per the CDC Children's BMI tool: below 5th percentile = underweight; 5th–85th = healthy; 85th–95th = overweight; above 95th = obese. Our calculator supports ages 5–100 but always consult a pediatrician for children.
Research & Trusted Sources
This tool is built on formulas from the world's most trusted health organizations and peer-reviewed journals. Click any source to verify:
Our free BMI calculator follows the exact formula endorsed by the World Health Organization, National Institutes of Health (NIH), and the CDC. Whether you need BMI for insurance, a fitness goal, or a doctor's visit — this tool provides everything in one place.
Unlike basic calculators, ours provides: WHO-classified BMI category, ideal weight range, estimated body fat % via the Deurenberg formula, TDEE calories via the Mifflin–St Jeor equation, macro breakdown, and evidence-based health tips with source links.
Medical Disclaimer: BMI is a screening tool, not a diagnostic measure. Always consult a qualified healthcare professional for medical advice.