Calculate your Body Mass Index

What is BMI?

BMI stands for body mass index which is a formula which relates body weight to height. This enables people to determine whether they are at a weight which is healthy for them. BMI can be divided into several categories and generally the higher your BMI, the greater your risk of a large range of medical problems.

BMI charts are calculated for adults only (separate charts are available for children’s weight and heights). Inaccuracies can occur if you're an athlete or very muscular as this can give you a higher BMI even if you have a healthy level of body fat and this BMI chart is not appropriate for women who are pregnant or breastfeeding, or people who are very frail.

As BMI is based on weight and height, by losing weight you will reduce your BMI and put yourself into a lower risk group. A healthy diet, including a balance of food groups, vitamins and minerals, is essential for a long and active life. Keeping it simple, body weight and shape are a balance of energy intake (dietary calorific content) against output (calorific burn from activity & exercise).


Someone with a BMI of below 18.5 is considered underweight. Whilst some people are naturally slim, being underweight from poor nutrition, or as a result of other disease, can have serious health risks. Illness associated with being underweight ranges from simple tiredness due to inadequate energy intake, through to reduced immunity to infections, anaemia, vitamin deficiencies, thinning of the bones, infertility and heart rhythm irregularities. If your BMI is under 18.5 you should discuss it with your doctor to ensure that you don’t have any illness causing the weight loss.


A BMI of 18.5 to 24.9 suggests a normal healthy weight. This means your body is not at risk of weight-related disease. You still need to ensure a balanced diet with plenty of fresh fruit, vegetables and good vitamin and mineral intake, but if your calorific intake is matching your energy output you will remain a normal weight.


With a BMI of 25 to 29.9 many people may only notice they are overweight when their clothes get tighter - by then the excess weight you're carrying will already have silently started to damage your blood vessels, hormone system and joints, raising your risk of diseases such as:

Although you may feel no different, you need to take action whilst the effects of being overweight can be reversed more easily - you need to gently reduce your calorific intake and increase your activity level. Crash diets don’t work - you need to change your lifestyle. Even slight changes can make a significant difference over time.


With a BMI of 30 to 35 you're now medically classified as obese - this means you're at high risk of weight related illness, such as:

But if you can lose even just a little weight your risk will drop - Just a five per cent weight loss (from 80kg to 76kg) has been shown to significantly reduce the health risks associated with obesity, such as reducing your cholesterol levels and blood pressure and giving you better blood sugar control


To have a BMI over 35 is considered as being very obese and this means that obesity-related illnesses could severely affect the quality of your life and shorten your lifespan by several years. By losing weight however you can improve many of the metabolic changes and reduce disease risks. If your BMI has reached 40 or more you're ‘morbidly obese’ - you will be 80 times more likely to develop type two diabetes than someone with a normal BMI, your lifespan will be shortened by over ten years and your quality of life will be reduced in many ways.

To discuss your individual nutritional needs please contact our CHNC registered Nutritionist and Nutritional Therapist email:

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