BMI Calculator | What's Your BMI? | WW UK

Get your BMI in seconds

BMI calculator

Body Mass Index (BMI) is a measure for weight-related health risk. Check yours with our BMI calculator below.

Understanding your BMI result

Under 18.5

Underweight. This could be a sign that you're not eating enough, or indicate underlying medical conditions. Your GP can help if you're underweight.

18.5 – 24.9*

Healthy weight. Keep up the good work!

25 – 29.9
Overweight. Building healthy habits, like eating healthily and being more active, can help you lose weight.
Obese. Building healthy habits, like eating healthily and being more active, can help you lose weight.
Calculate your BMI
Find out more

Our customised weight loss plans can help lower your BMI.

What is BMI and what does it measure?

BMI is a simple measure of weight in relation to height. It estimates percentage of body fat, and is used to broadly measure weight-related health risk.

A higher percentage of body fat is proven to be associated with increased risk for developing certain diseases such as heart disease, high blood pressure, type 2 diabetes, breathing problems, certain cancers and a higher risk of early death.

Underweight is the range of weight that is lower than what is generally considered healthy for a given height. It may indicate underlying medical conditions or an eating disorder, plus higher risk for conditions such as osteoporosis.

How accurate is a BMI calculator?

It's important to recognise that BMI alone may not be the most accurate measure of weight-related health risk. BMI doesn't take into account gender, age or muscle mass - which means athletes and bodybuilders would be classed as overweight or obese.

It also doesn't take fat distribution into account. This is important because accumulation of fat in the upper part of the body versus the lower part of the body is associated with an increased risk for coronary heart disease and type 2 diabetes.

Think of it like this: one person may carry a lot of fat around their middle but not in their legs, while another could have the same amount of fat but distributed more evenly around their body. Both may have the same BMI, but the first person may be a higher health risk. 

BMI alone may not be the best measure of weight-related health risks, but it does provide a good starting point for most people. Find out more about the limitations of BMI.

Lower your BMI with WW

BMI continues to be the best estimation of weight-related health risk because of its scalability and accessibility. It's a simple calculation based on easily measured values that is relatively easy to understand.  

Stepping on the scales may seem daunting, but once you know your weight, you’re in a good place to make an action plan for success. The WW programme offers a safe and sustainable way to lose weight, at a rate of around 1-2lb per week, without having to count calories or go hungry. Faster weight loss is often unsustainable - check out these 5 things to consider before trying to lose weight fast.

Start eating better than ever

**WW is committed to be a responsible provider of programmes and services that inspire healthy habits for real life. We encourage people to attain ultimate weight goals that are realistic and sustainable. We have specifically chosen to be conservative in our policies and procedures and, as such, have a “floor” on our healthy weight range of a BMI of 20. This is done for two reasons. First, the weight ranges serve to assess eligibility for membership and require that a potential member be at least 5 pounds above the minimum weight. If we used a BMI of 18.5, individuals who are already at a lower weight would be eligible to join. Second, we encourage people to attain ultimate weight goals that are realistic and sustainable.