BMI Index & Range

What is BMI?

Body Mass Index (BMI) is a simple numerical measure calculated from your height and weight. First developed by Belgian mathematician Adolphe Quetelet in the 1830s, it has since become the most widely used screening tool for weight categories across the world. The World Health Organization (WHO) and health authorities in nearly every country use BMI as a first-line assessment of whether a person falls into an underweight, healthy, overweight, or obese category.

BMI is not a direct measure of body fat — it is a weight-to-height ratio. However, research consistently shows it correlates well with body fat percentage in most adults, making it a useful and practical starting point for health assessments.

How to Use This BMI Calculator

Our BMI calculator gives you an instant, personalised result in under 30 seconds. Select your gender and age group, enter your height and weight, and your BMI score, health category, and ideal weight range update instantly. For children and teenagers, the calculator automatically applies age-adjusted thresholds because growing bodies have different healthy ranges.

Understanding the BMI Formula

For example, a person who is 175cm tall and weighs 70kg has a BMI of 70 ÷ (1.75 × 1.75) = 22.9 — which falls in the healthy weight range.

What Your BMI Score Means

The WHO defines four standard BMI categories for adults aged 20 and over:

BMI for Children and Teenagers

For children aged 2–19, BMI is interpreted differently. Rather than fixed cut-off numbers, paediatricians use BMI-for-age percentiles — comparing a child's BMI to other children of the same age and sex. Our calculator uses simplified age-adjusted thresholds to give a general indication, but for precise paediatric assessment, always consult a doctor.

Limitations of BMI — What It Cannot Tell You

• It ignores muscle mass: A trained athlete may have a high BMI while having very low body fat.
• It does not measure fat distribution: Abdominal fat carries a higher health risk than fat stored elsewhere, but BMI cannot detect this.
• It varies across ethnicities: People of Asian descent face higher health risks at lower BMI thresholds.
• Less accurate for older adults: Muscle loss with ageing means older adults may have a normal BMI but high body fat.

How to Reach a Healthy BMI

If you are overweight or obese:

• Calculate your TDEE to understand your maintenance calories
• Use the Calorie Deficit Calculator to set a safe daily target
• Aim for 0.5kg weight loss per week — this pace preserves muscle mass best
• Use our Macro Calculator for a balanced nutrition split

If you are underweight:

• Increase calorie intake gradually with nutrient-dense foods
• Add resistance training to build healthy muscle mass
• Use our Protein Intake Calculator to set adequate protein targets

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