Learn what your BMI (Body Mass Index) is to find out if you’re eligible for weight loss treatment.

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.

What is BMI?

Your BMI (body mass index) is a number that indicates whether you are underweight, at a healthy weight, overweight, or obese, relative to your height. It is a screening tool that can help estimate your body fat using your height and weight. It allows health care professionals to assess your risk of weight-related disease alongside other measurements.

How is BMI calculated?

Your BMI is calculated by dividing your weight in kilograms (kg) by your height in metres squared (m2). So, you’ll need to know your height and weight to use the BMI calculator.

Clinically, your BMI is used to assess if your weight is healthy for your height. It can be used to assess your risk of certain conditions. For example, a high BMI is associated with an increased risk of developing heart disease, type 2 diabetes and high blood pressure.

Although calculating BMI is a useful tool, it is not accurate for everyone. For example, if you’re very muscular, you may have a high BMI and even fall into the overweight category because muscle is denser than fat, so it adds extra kilos to your body weight.

Your ethnic background can also influence your BMI. If you are from a South Asian, Chinese, Black African, or African-Caribbean background, there are lower thresholds for you to meet. A BMI of 23 or above is classed as overweight and 27.5 or above as obese in these demographics.

BMI is also less useful during pregnancy. Although you may start a pregnancy at a healthy weight, as you gain weight, the BMI calculation can become less useful.

Calculating your BMI is useful because it can help you make important decisions about your health and lifestyle, especially regarding your weight. It can help you understand if you are underweight, overweight, or at a healthy weight for your height, whether you may be at an increased risk of certain health conditions, or if you may be suitable for weight loss medication. In this section, we’ll explain what your BMI score means for you.

What should I do if my BMI is under 18.5?

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.

What should I do if my BMI is between 18.5 and 25?

A BMI between 18.5 and 25 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.

If you are at the lower end of the range, you are close to falling into the underweight category for your height. So, it is important that you maintain a healthy, balanced diet and ensure that you are not in a calorie deficit, where you burn more calories than you consume.

If your BMI is at the upper end of the range, although you are at a healthy weight for your height, it is important that you avoid any further weight gain. Make sure you meet the weekly exercise requirement of at least 150 minutes of moderate-intensity exercise each week and eat healthily, avoiding processed and high-fat foods, which have little nutritional value.

If you are of an ethnic background, a healthy BMI is considered to be between 18.5 and 22.9. If you have a BMI of 23 or above, this is considered overweight, and you should follow the advice below.

Being overweight or obese 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 or obese 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. 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.

Your BMI is one of the main factors used to assess whether you may be suitable for prescription weight loss treatments, such as Mounjaro or Wegovy. Whether you can get weight loss medication will also depend on your medical history, current health, and the treatment you are requesting. A doctor will always decide whether weight loss medication is safe for you.

The different BMI ranges to qualify for weight loss treatment in the UK are:

Your BMI will also be used to see if you are suitable for weight loss pills, such as orlistat (Xenical) and Mysimba.

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.

Because of this, doctors may use other measurements alongside BMI to better assess your health risks, such as:

1. Waist-to-height ratio. It is calculated by dividing your waist size by your height – This measures how body fat is distributed around your waist. Carrying more weight around your stomach is linked to an increased chance of heart disease and type 2 diabetes.
2. Waist circumference – This measurement identifies excess fat around your stomach, which increases the chance of heart and metabolic conditions, like type 2 diabetes.
3. Waist-to-hip ratio – Compares your waist circumference to your hip circumference to understand your body fat distribution. A higher ratio indicates a higher amount of fat around your stomach, which is associated with a greater chance of getting heart disease or type 2 diabetes.
4. Body fat percentage – This estimates how much of your body is made up of fat tissue compared to muscle, bone, and water.
5. Body composition – This measurement is used to tell you the amount of fat, muscle, lean tissue, and water in the body to give a wider view of your overall health.

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.