What is a healthy BMI?

A healthy BMI is typically between 18.5 and 24.9. This range is associated with lower risk of weight-related health problems.

Is BMI accurate for everyone?

BMI is a general indicator and may not be accurate for athletes, elderly individuals, pregnant women, or people with high muscle mass.

How is BMI calculated?

BMI is calculated by dividing your weight in kilograms by the square of your height in meters. For imperial units, divide weight in pounds by height in inches squared, then multiply by 703.

What are the BMI categories?

Underweight: BMI less than 18.5. Normal weight: BMI 18.5 to 24.9. Overweight: BMI 25 to 29.9. Obese: BMI 30 or greater.

Can children use this BMI calculator?

This calculator is designed for adults. Children and teens should use age- and sex-specific BMI percentile charts for accurate assessment.

Does BMI predict health outcomes?

While BMI correlates with health risks like heart disease and diabetes, it's just one factor. Lifestyle, diet, and genetics also play important roles in overall health.

BMI Calculator

Weight (kg)

Height (cm)

Weight (lbs)

Height (feet)

Height (inches)

Your BMI

< 18.5

18.5-24.9

25-29.9

30+

Underweight Normal Overweight Obese

What does this mean?

💡 Your numbers in context

Est. daily calories (sedentary)

To reach healthy BMI mid-range

Calorie estimate uses a simplified BMR formula. Consult a healthcare professional for personalised advice.

Your Healthy Weight Range

Minimum (BMI 18.5)

Maximum (BMI 24.9)

How BMI Is Calculated

BMI (Body Mass Index) was developed by Belgian statistician Adolphe Quetelet in the 1830s as a population-level tool, not an individual health diagnostic. It divides weight by the square of height to produce a single number that roughly correlates with body fat at a population level.

Metric formula

              BMI = weight (kg) ÷ height (m)²

Imperial formula

              BMI = (weight lbs ÷ height in²) × 703

Worked example

Person weighing 75 kg, height 1.78 m:
BMI = 75 ÷ (1.78 × 1.78) = 75 ÷ 3.1684 = 23.7 — Normal weight.

BMI Categories Explained

The WHO and most national health agencies use these four adult thresholds. Note that some ethnic populations have different risk profiles at lower BMI values (see below).

Category	BMI range	Health context
Underweight	Below 18.5	May indicate nutritional deficiency
Normal weight	18.5 – 24.9	Associated with lowest health risk
Overweight	25 – 29.9	Moderately elevated risk factors
Obese	30 and above	Higher risk of metabolic disease

What BMI Doesn't Tell You

BMI is a useful first screen but is widely acknowledged to have significant limitations. A 2022 study in PLOS ONE found it misclassifies health status in over 30% of adults when compared to direct body fat measurement. Here's what it misses:

Muscle vs. fat: Muscle is denser than fat. A fit 90 kg athlete at 1.80 m has a BMI of 27.8 (overweight), yet may have very low body fat. BMI cannot distinguish the two.

Fat distribution: Where you store fat matters more than total weight. Central (abdominal) fat is more metabolically harmful than fat stored elsewhere. Waist circumference above 94 cm (men) or 80 cm (women) is an independent risk indicator BMI doesn't capture.

Age and sex: Women naturally carry more body fat than men at the same BMI. Older adults typically have more fat and less muscle for the same BMI as younger adults. Neither adjustment is built into standard BMI.

Ethnicity thresholds: South Asian, Chinese, and some other populations face higher metabolic risk at lower BMI values. Many clinicians use action thresholds of 23 (overweight) and 27.5 (obese) for these groups, rather than 25 and 30.

BMI Calculator FAQ

Not necessarily. BMI is a population screen, not a personal diagnosis. Many people in the 25–29.9 range have no metabolic risk factors at all. What matters more is waist measurement, cardiorespiratory fitness, blood pressure, blood glucose, and cholesterol. A BMI of 27 in a person who exercises regularly, eats well, and has normal blood markers is very different from the same BMI in someone who is sedentary. Speak to your GP for a full picture.

Yes — this is the flip side. A person can be "normal weight" by BMI but have high body fat percentage and low muscle mass. This is sometimes called "skinny fat" or metabolically obese normal weight (MONW). Research shows this profile carries similar cardiovascular risks to obesity. Waist circumference, fitness levels, and metabolic markers matter regardless of BMI.

Divide your weight in kg by your height in metres, then divide again by your height. Example: 80 kg, 1.75 m → 80 ÷ 1.75 = 45.71 → 45.71 ÷ 1.75 = 26.1. For imperial: multiply weight (lbs) by 703, then divide by height (inches) squared.

Most evidence suggests a slightly higher BMI (around 22–27) is associated with better outcomes in adults over 65. Being underweight in older age carries significant risks including falls, fractures, and reduced immune function. The "overweight" category may actually be protective in this group.

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Health Information Disclaimer

This calculator is for informational purposes only and is not a substitute for professional medical advice. Always consult a qualified healthcare provider for health concerns. Last reviewed: April 2026.