Calculate your Body Mass Index instantly and find out whether you are underweight, normal weight, overweight or obese. This free BMI calculator works for men and women of all ages and supports both metric and imperial units.
What Is BMI ?
BMI stands for Body Mass Index. It is a number calculated from your height and weight that gives a general indication of whether your body weight is healthy for your height. BMI is widely used by doctors, nutritionists and health professionals around the world as a quick screening tool for weight-related health risks.
How to Use This BMI Calculator
Select your unit system — metric for kilograms and centimetres or imperial for pounds and feet. Select your gender and enter your age. Enter your weight and height. Then click Calculate My BMI. Your results appear instantly.
What This BMI Calculator Shows You
This calculator shows your BMI score, your health category, your ideal weight range for your height, how much weight you may need to lose or gain to reach the healthy range, your BMI Prime score, your Ponderal Index, and a personalised health insight based on your result.
BMI Categories Explained
Underweight is a BMI below 18.5. This may indicate that you are not getting enough nutrition or that there is an underlying health condition worth discussing with a doctor.
Normal weight is a BMI between 18.5 and 24.9. This is considered the healthy range for most adults. Maintaining this range through a balanced diet and regular exercise is recommended.
Overweight is a BMI between 25 and 29.9. This may increase the risk of conditions like high blood pressure and type 2 diabetes. Small consistent lifestyle changes can make a significant difference.
Obese Class I is a BMI between 30 and 34.9. This range carries a higher risk of serious health conditions and consulting a healthcare professional for a weight management plan is recommended.
Obese Class II and above is a BMI of 35 or higher. Medical supervision is strongly advised at this level.
BMI for Men vs Women
BMI uses the same formula for men and women. However doctors sometimes interpret BMI results slightly differently based on gender because men and women tend to carry body fat differently. Women naturally carry more body fat than men at the same BMI. This calculator takes your gender into account when displaying your results.
Limitations of BMI
BMI is a useful screening tool but it has limitations. It does not directly measure body fat and does not account for muscle mass. A very muscular person like an athlete may have a high BMI but low body fat. Similarly an older person may have a normal BMI but carry excess fat. Always use BMI as one indicator among several and consult a doctor for a full health assessment.
What Is a Healthy BMI for Adults
For most adults a BMI between 18.5 and 24.9 is considered healthy. For adults over 65 a slightly higher BMI may be acceptable as some research suggests a BMI between 25 and 27 may be protective in older age. Children and teenagers use a different BMI scale that accounts for age and gender.
Frequently Asked Questions
What is a good BMI score? A BMI between 18.5 and 24.9 is generally considered healthy for most adults. A score below 18.5 is underweight and a score of 25 or above is overweight.
How is BMI calculated? BMI is calculated by dividing your weight in kilograms by your height in metres squared. In imperial units the formula is weight in pounds divided by height in inches squared multiplied by 703.
Is BMI accurate for everyone? BMI is a general screening tool and is not perfectly accurate for everyone. Athletes with high muscle mass may show a high BMI despite being very healthy. Elderly people may show a normal BMI despite having excess body fat. It is best used alongside other health measures.
What is BMI Prime? BMI Prime is your BMI divided by 25 which is the upper limit of the normal range. A BMI Prime of less than 1.0 means you are in the healthy range. A value above 1.0 means you are above the healthy range.
What is the Ponderal Index? The Ponderal Index is similar to BMI but uses the cube of height rather than the square. It is sometimes considered more accurate for very tall or very short people.
Is this BMI calculator free? Yes completely free. No sign up, no login, no limits. Works for metric and imperial units.
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Last updated: March 2026 · Free tool by AllTheTools.com