BMI Calculator — Body Mass Index
Calculate your BMI using the WHO standard, see your healthy weight range, and get evidence-based next steps for nutrition — including your personalised protein target.
Understanding Your BMI — and What to Do Next
BMI is a starting point, not a destination. A high BMI tells you that you may have excess body fat relative to your height — but it doesn't tell you how much, where it's located, or what your body composition actually looks like. The most actionable next step after checking your BMI is to find out your protein target and calorie needs.
If BMI is Underweight (<18.5)
Focus on increasing total calorie intake and protein (1.6–2.2 g/kg) alongside resistance training. A small calorie surplus of 200–400 kcal/day supports gradual, lean mass gain.
If BMI is Normal (18.5–24.9)
Maintain current calories at TDEE. Optimise protein for your goal (muscle gain, performance, or general health). Use the Macro Calculator for a full picture.
If BMI is Overweight (25–29.9)
A moderate calorie deficit (10–20% below TDEE) combined with high protein (1.2–2.0 g/kg) and resistance training is the most effective approach for sustainable fat loss.
If BMI is Obese (≥30)
Same principles apply: calorie deficit + high protein. Using lean body mass (not total weight) for protein targets avoids over-eating protein. Consulting a dietitian is recommended.
Frequently Asked Questions
What is BMI?
BMI (Body Mass Index) is a screening measure that estimates body fatness using height and weight. It is calculated as weight (kg) divided by height (m) squared. The WHO classifies BMI into four categories: underweight (<18.5), normal weight (18.5–24.9), overweight (25–29.9), and obese (≥30). BMI is a population-level tool, not a diagnostic measure for individuals.
Is BMI accurate?
BMI is a useful screening tool at the population level but has significant limitations at the individual level. It cannot distinguish between muscle and fat mass, so muscular athletes often have 'overweight' BMIs despite having low body fat. Conversely, people with low muscle mass ('skinny fat') can have a 'normal' BMI while carrying metabolically harmful visceral fat. Use BMI alongside other measures like waist circumference and body fat percentage for a fuller picture.
What is a healthy BMI?
The WHO defines a healthy BMI as 18.5–24.9. Some researchers suggest the lower end of this range (18.5–22) may be optimal for all-cause mortality based on large prospective studies. However, for muscular individuals, a BMI up to 27 may be perfectly healthy. BMI thresholds also differ by ethnicity: Asian populations have lower obesity thresholds (23 for overweight, 27.5 for obese).
What should I do if my BMI is high?
If your BMI is in the overweight or obese range, the most evidence-backed first steps are: (1) calculate your TDEE and create a moderate calorie deficit (10–20%), (2) increase protein intake to 1.2–1.6 g/kg to preserve muscle during fat loss, (3) add resistance training to maintain lean mass, and (4) consult your doctor or a registered dietitian for personalised guidance. Sustainable fat loss of 0.5–1 kg/week is achievable and maintainable.
What is a healthy BMI for women vs men?
The standard WHO BMI categories (18.5–24.9 for healthy weight) apply to both sexes. However, women naturally carry more body fat than men at the same BMI — a woman with a BMI of 22 will have a higher body fat percentage than a man with the same BMI. For clinical evaluation, body fat percentage cut-offs differ by sex: >32% body fat is classified as obese for women vs >25% for men.