⚖️ BMI Tool

Free Online BMI Calculator

Calculate your Body Mass Index instantly. Get ideal weight, calorie needs, body fat estimate and personalised health tips.

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Body Mass Index
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UnderweightNormalOverweightObese
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Ideal Weight Range
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Est. Body Fat %
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Lean Body Mass
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BMR (cal/day)
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Weight to lose/gain to reach Normal BMI
🔥 Daily Calorie Needs (TDEE)
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Weight Loss
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Maintain Weight
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Weight Gain
💡 Personalised Health Tips

What Is BMI and How Is It Calculated?

Body Mass Index (BMI) is a simple yet widely used numerical value derived from a person's weight and height. It was developed in the 19th century by Belgian mathematician Adolphe Quetelet and has since become one of the most common screening tools used by healthcare professionals worldwide to assess whether a person's weight falls within a healthy range relative to their height.

The formula is straightforward: BMI equals your weight in kilograms divided by the square of your height in meters (kg/m²). For imperial measurements, the formula uses pounds and inches with a conversion factor. While BMI does not directly measure body fat, research has shown it correlates reasonably well with more direct measures of body fat for most adults.

BMI RangeCategoryHealth Risk
Below 18.5UnderweightIncreased risk of nutritional deficiencies
18.5 – 24.9Normal WeightLowest health risk
25.0 – 29.9OverweightModerate increased risk
30.0 – 34.9Obese Class IHigh risk
35.0 and aboveObese Class II–IIIVery high risk

It is important to understand that BMI is a screening tool, not a diagnostic instrument. Athletes with high muscle mass may have a high BMI without excess fat, while older adults may have a normal BMI but carry too much body fat. Always consult a healthcare professional for a comprehensive health assessment.

How to Use This BMI Calculator

Our BMI calculator is designed to be fast, accurate, and easy to use. It goes far beyond a basic BMI reading — providing ideal weight range, estimated body fat percentage, lean body mass, basal metabolic rate, daily calorie needs and personalised health tips, all in seconds. Follow these simple steps:

  1. 1
    Choose your unit systemUse the toggle at the top to switch between Metric (kilograms and centimetres) or Imperial (pounds, feet and inches) — whichever you are most comfortable with.
  2. 2
    Enter your ageType your current age in years. Age is used to fine-tune body fat estimation and basal metabolic rate calculations for greater accuracy.
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    Select your genderGender affects BMI interpretation and body fat percentage estimation, as men and women naturally carry fat differently. Choose Male or Female from the dropdown.
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    Select your activity levelChoose how active you are in daily life — from sedentary (desk job, little exercise) to extra active (hard exercise or physical job). This is used to calculate your Total Daily Energy Expenditure (TDEE).
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    Enter your weight and heightInput your current weight and height accurately. For imperial, enter feet and inches separately. Use a scale and measuring tape for best results.
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    Tap Calculate BMIHit the button and instantly receive your full results — BMI score with visual scale, category badge, ideal weight range, body fat estimate, calorie needs and personalised health recommendations.

Benefits of Tracking Your BMI

Regularly monitoring your BMI is one of the simplest ways to keep track of your overall health and weight management progress. While it is not perfect, it provides a reliable starting point for understanding your body composition and setting realistic fitness goals.

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Set Realistic Goals
Know exactly how much weight you need to lose or gain to reach a healthy BMI range, making your fitness journey more focused and achievable.
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Monitor Heart Health
Higher BMI is linked to increased risk of heart disease, hypertension and type 2 diabetes. Tracking it helps you stay aware of these risks early.
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Optimise Your Nutrition
With your personalised calorie needs (TDEE), you can structure your diet for weight loss, maintenance or muscle gain with precision.
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Track Progress Over Time
Recalculate your BMI monthly to see how your body is changing in response to diet and exercise, keeping you motivated and on track.
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Prepare for Doctor Visits
Come to medical appointments informed. Knowing your BMI and body metrics helps you have more productive conversations with your healthcare provider.
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Understand Lean Mass
Our calculator also estimates your lean body mass — the weight of everything except fat — which is crucial for athletes and those focused on strength training.

Remember, BMI is a starting point. Combine it with waist circumference measurements, body fat percentage testing and regular medical check-ups for a complete picture of your health.

Frequently Asked Questions
BMI is a useful general screening tool but has limitations. It does not distinguish between muscle and fat, so athletes and bodybuilders may show a high BMI despite having very low body fat. It also may not accurately reflect health risks for older adults, pregnant women or people from certain ethnic backgrounds. Always use BMI alongside other health indicators.
For most adults aged 18 and over, a BMI between 18.5 and 24.9 is considered healthy. Below 18.5 is classified as underweight, 25 to 29.9 as overweight, and 30 or above as obese. However, these thresholds may vary slightly for different ethnic groups — for example, health risks for South Asian populations may begin at a lower BMI.
Our calculator uses the Deurenberg formula, which estimates body fat percentage based on BMI, age and gender. While not as precise as DEXA scans or hydrostatic weighing, it provides a reasonable estimate for most people. The formula accounts for the fact that women naturally carry more body fat than men, and that body fat tends to increase with age even when BMI stays the same.
BMR stands for Basal Metabolic Rate — the number of calories your body needs at complete rest just to maintain basic functions like breathing, circulation and cell production. We calculate it using the Mifflin-St Jeor equation, which is considered the most accurate for most people. Multiply your BMR by your activity factor to get your Total Daily Energy Expenditure (TDEE), which tells you how many calories you actually need each day.
For general health monitoring, checking your BMI once a month is sufficient to track trends without becoming obsessive. If you are actively trying to lose or gain weight, you might check every two weeks alongside other metrics like waist measurements and progress photos. Daily fluctuations in weight are normal due to water retention, food intake and other factors, so avoid checking too frequently.
Yes — completely. All calculations are performed entirely in your browser using JavaScript. No data you enter (age, weight, height, gender) is ever sent to any server or stored anywhere. Your information never leaves your device, making this tool 100% private and safe to use.
The ideal weight range is calculated by finding the weight values that correspond to a BMI of exactly 18.5 (lower bound) and 24.9 (upper bound) for your specific height. This gives you a personalised healthy weight range rather than a generic number, making it far more useful as a practical goal for your body type.