BMI Calculator

About the BMI Calculator

It's important to note that BMI doesn't directly measure body fat, but it's a useful screening tool to identify potential weight related health risks and guide further discussion with your doctor.

Body Mass Index (BMI) is a simple way to see whether a person's weight is appropriate for their height. It helps to determine whether someone is underweight, normal weight, overweight, or obese. A BMI calculator works by taking a person's weight and height, which is used to calculate their BMI. Once you know your BMI, you can compare it to the average BMI considered to be ‘normal’ weight to understand where you fall. For example, a BMI below 18.5 is considered underweight, between 18.5 and 24.9 is normal weight, between 25 and 29.9 is overweight, and 30 or higher is classified as obese.

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Is Body Mass Index Reliable?

Body Mass Index (BMI) is a helpful tool for determining weight related health risks, but it is not a complete indicator of your overall health. Anyone can use a BMI calculator to determine which weight category they belong to, but there are some potential blind spots.

BMI does not differentiate between muscle mass and body fat, meaning that athletes or people with higher muscle mass may have a higher BMI, even though they are healthy and not overweight. It also doesn't take into account other factors that can influence health, such as age, gender, ethnicity, or overall body composition.

While a BMI calculator provides a quick and straightforward way to determine your weight category, it should be used in conjunction with other information and interpreted by a doctor for a more thorough understanding of your overall health.

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What are the BMI weight ranges?

Under 18.5 (underweight)

A BMI below 18.5 indicates that your weight is lower than what is considered healthy for your height. Being underweight can lead to nutritional deficiencies, weakened immune function, and potential health issues. If you have a BMI in this range, you should speak to your doctor to address any underlying causes and develop a plan to reach a healthier weight.

Between 18.5 and 24.9 (healthy weight)

A BMI between 18.5 and 24.9 suggests that your weight is proportionate to your height, and you are likely at a lower risk of weight-related health problems. However, even within this range, it's important to maintain a balanced diet, engage in regular physical activity, and monitor your overall wellbeing to support good long-term health.

Between 25 and 29.9 (overweight)

A BMI between 25 and 29.9 classifies you as overweight. This means that your weight exceeds the recommended level for your height, and you may have an increased risk of developing conditions like heart disease, type 2 diabetes, and certain cancers. If your BMI is in this category, adopting a healthier lifestyle through proper nutrition, exercise, and seeking guidance from your doctor can help manage your weight and improve your overall health.

Over 30 (obese)

A BMI of 30 or higher indicates obesity. This means your weight is very high relative to your height, which can significantly impact your health. Obesity is associated with a higher risk of severe health problems, including heart disease, stroke, high blood pressure, type 2 diabetes, and joint issues. If your BMI falls into the obese category, your doctor can help you create a personalised weight management plan, to reduce the associated health risks.

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Measuring waist to height ratio

A waist to height ratio is a measurement that compares your waist circumference to your height and provides insight into how fat is distributed in your body. To calculate waist to height ratio:

Measure your waist circumference (this is usually above your hip bone, below your ribs).
Divide your waist circumference by your height in the same unit of measurement (e.g. centimetres or inches).

A waist to height ratio of 0.5 or higher indicates that your waist circumference is equal to or larger than half of your height, which may suggest an increased risk of health problems associated with excess abdominal fat.

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What are the risks associated with being underweight?

Being underweight can pose several health risks due to insufficient body mass and potential nutrient deficiencies. Some common risks associated with being underweight include:

nutritional deficiencies
weakened immune function
osteoporosis (a condition where bones become weak and prone to fractures)
decreased muscle strength
hormonal imbalances
fatigue and weakness
impaired growth and development
mental health concerns

It's important to address the underlying causes of being underweight and work towards achieving a healthy weight through a balanced and nutritious diet, regular exercise, and medical support if needed. Your doctor can help identify any specific nutrient deficiencies and develop a personalised plan to improve your overall health and well-being.

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What are the risks associated with being overweight?

Being overweight can lead to various health risks and increase the likelihood of developing several chronic conditions. Some common risks associated with overweight individuals include:

high blood pressure (hypertension)
coronary heart disease (CHD)
stroke
type 2 diabetes
sleep apnoea
joint problems
fatty liver disease
certain cancers (including breast, colon, endometrial, and kidney)
mental health issues

If you’re overweight it’s important to take steps towards achieving a healthier weight through a combination of balanced nutrition, regular physical activity, and seeking guidance from your doctor. By managing your weight effectively, you can significantly reduce your risk of developing these health complications and improve your overall wellbeing.

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