BMI Calculator

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Note: BMI is a quick screening metric—athletes and individuals with high muscle mass may have misleading results. Always seek professional advice for a full health assessment.

BMI is a quick, low-cost way to gauge body-fat levels by dividing your weight (kg) by the square of your height (m²). Health agencies—including the World Health Organization (WHO) and U.S. CDC—use it as a first-pass screening tool for nutrition- or weight-related problems.

Category	BMI (kg/m²)	Health Note
Underweight	< 18.5	Possible nutrient deficiency
Healthy / Normal	18.5 – 24.9	Lowest disease risk
Overweight	25 – 29.9	Higher cardiometabolic risk
Obesity Class I	30 – 34.9	Substantially higher risk
Obesity Class II	35 – 39.9	Severe risk
Obesity Class III	≥ 40	Very severe risk

3. Global Obesity Snapshot (Latest WHO 2024 data)

2.5 billion adults—43 % of everyone aged ≥ 18—were overweight in 2022. Almost 890 million lived with obesity.
Adult obesity has more than doubled since 1990; adolescent obesity (ages 5-19) has quadrupled.
Regional picture:
- Americas: ~ 67 % of adults are overweight.
- Southeast Asia & Africa: ~ 31 %.
Looking ahead, the World Obesity Federation projects 1.5 billion adults with obesity by 2035, with four out of five cases in low- and middle-income countries. worldobesity.org

4. Why Your BMI Matters

Cross-country studies consistently link higher BMI to type 2 diabetes, hypertension, coronary heart disease, stroke, some cancers, and premature death. Conversely, a BMI below 18.5 may signal under-nutrition, osteoporosis risk, or weakened immunity. Keeping BMI in the 18.5–24.9 band is associated with better quality of life and lower healthcare costs.

5. Caveats & Evolving Thinking

Muscle vs. fat: Athletes or very muscular people may fall into the “overweight” bracket despite low body-fat percentage.
Ageing: Adults 65+ often lose muscle and gain visceral fat, so BMI can under-read risk.
Fat distribution counts: A simple waist-to-height ratio (keep it < 0.5) can flag central obesity and cardiovascular risk more accurately than BMI alone. NICE added this metric to its 2024 guidance on weight assessment.

6. Habits That Keep BMI (and Waistlines) in Check

Audit your plate: Aim for half vegetables, one-quarter lean protein, one-quarter whole-grain carbs.
Move with intent: At least 150 minutes moderate exercise (or 75 minutes vigorous) each week.
Cut liquid calories: One daily sugary-drink swap for water trims ~150 kcal.
Prioritise sleep: Fewer than six hours a night can nudge hormones that drive weight gain.
Stay consistent: Re-calculate BMI—or waist-to-height ratio—every month if you’re actively changing weight; quarterly otherwise.
Seek expert support: A registered dietitian or doctor can factor in muscle mass, medical conditions, and cultural dietary needs.

Is BMI accurate for everyone?

BMI works for most adults, but it can misclassify athletes, pregnant people, and older adults with low muscle mass. Combine it with waist measurement for a fuller risk picture.

What is a healthy BMI range?

For adults aged 18 +, 18.5 – 24.9 kg/m² is linked to the lowest risk of chronic disease.

How often should I track BMI?

Monthly if you're actively changing weight; quarterly snapshots are fine otherwise.

Does BMI apply to children?

Yes, but paediatric BMI uses age- and sex-specific percentiles rather than adult cut-offs. A paediatrician can interpret the growth chart accurately.

Can I lower my BMI quickly?

Sustainable weight loss of 0.5 – 1 kg per week is safer than crash diets and more likely to last. Pair balanced nutrition with regular exercise and enough sleep.