What does BMI (body mass index) mean? 

BMI (body mass index) is a measurement that uses your height and weight to estimate whether your body weight falls within a healthy range. It is commonly used by medical professionals and can also be calculated at home to place you into the following weight categories: 

• Underweight  
• Healthy weight  
• Overweight  
• Obese  
• Severely obese  

Your BMI is calculated with the formula:  

Weight (kg) divided by height (m)  

Our calculator does this for you, so you don’t need to worry about the maths. 

What is the ideal BMI? 

The ideal BMI is a BMI score of 18.5 to 24.9. This falls under the ‘healthy weight’ category. 

Ideal BMI for men compared to women 

For adults, a healthy BMI typically falls between 18.5 and 24.9. A BMI below 18.5 is classed as underweight, while a BMI of 25 or above is considered overweight. 

These ranges apply to both men and women. However, the healthy weight ranges used within the calculation can differ due to natural variations in body composition. 

What your BMI score means 

Your BMI score tells you if you’re at a healthy weight for your height. You’re given a score which puts you in one of five weight categories. These are:  

Underweight 

Being underweight means you may not be getting enough energy or nutrients to fuel your body. This can lead to fatigue and various health conditions, such as a weakened immune system and malnutrition. 

Healthy Weight 

Maintaining a healthy weight is important. Staying within the healthy weight range can vastly decrease your chances of serious health issues.  

Overweight, obesity (class 1-2) and severe obesity (class 3) 

The overweight, obese and severe obesity categories indicate that you have too much body fat for your height. Overweight and obesity are linked to an increased risk of various health problems, including heart disease, type 2 diabetes, and certain cancers. 

Do I need medical support if I’m overweight? 

If you haven’t already developed the health issues associated with being obese. Medical help can be beneficial for those who have adapted to a healthier lifestyle and whose weight/BMI is not shifting.  

Medical help will also be necessary if health issues like diabetes or high blood pressure occur.   

Medicines such as Wegovy (semaglutide), Mounjaro (tirzepatide), liraglutide and Orlistat can help manage obesity and diabetes. 

What BMI do I need for weight loss medication? 

To be eligible for weight loss medication, like Mounjaor or Wegovy, you usually need to  have a BMI of 30 or above, or a BMI of 27 or above alongside conditions like h h blood pressure, high cholesterol, or type 2 diabetes. 

You might find that NHS pathways use stricter criteria, with access often prioritised for people with higher BMIs or more complex health needs, and usually through specialist weight management services.  

What matters most is understanding your BMI so you know where you stand and can begin making positive changes. It is not about labels, but about building a clearer picture of your health and what support could benefit you. 

If treatment is appropriate, our clinicians will carry out a thorough assessment to make sure medication is safe and suitable for you. And remember, medication is only one part of the journey. With the right guidance, sustainable habits, and ongoing support, you can make meaningful progress towards your long term health goals. 

Is BMI accurate? 

In some instances, your BMI score can be slightly inaccurate. Some people who may have an inaccurate BMI score are:  

• Muscular people  
• Some Black & Asian ethnic groups  
• Pregnant women  
• Children  
• People over age 60 

Muscular people 

Your weight in kg on a scale doesn’t account for muscle mass compared to body fat, and since muscle weighs more than fat (as it’s denser) your weight may seem heavy. Having very little body fat but a high BMI score is inaccurate. 

Black & Asian ethnic groups 

BMI scores are primarily based on data from white European populations and don’t account for the differences in body composition or fat distribution among various ethnicities. 

Pregnant women 

Your BMI score doesn’t account for weight gained during pregnancy (or the weight of the baby), nor does it consider the significant change in body composition. If you do decide to check your BMI score whilst pregnant, bear in mind that it will be inaccurate, and weight gain during pregnancy is natural and healthy. 

Children 

While the formula for calculating a person’s BMI is the same for children, it needs to be age and sex specific. It also doesn’t take bone density into consideration. 

People over 60 

BMI scores in people over 60 are inaccurate as they don’t take into consideration age-related changes in body composition, such as the decrease in muscle mass and increase in body fat.