What BMI does and does not tell you
Body mass index relates your weight to your height with one number. Health agencies use it because it is easy to measure and correlates with health risks across large groups of people.
For an individual, it is a starting point for a conversation, not a verdict. It ignores muscle, bone density, age and body shape, so use it alongside other measures such as waist size, fitness and blood tests.
Reading your healthy weight range
The range shown is the weight at which your height would give a BMI between 18.5 and 24.9. If you are outside it, the calculator shows roughly how much you would need to change to enter it. That is a useful guide, but you do not need to hit the exact range to be healthy.
If you want to plan a change in weight, the TDEE and calorie calculators turn a goal into a daily energy target.
When to see a professional
A doctor can interpret BMI in the context of your age, family history and health. Speak to one before making big changes to your diet, especially if you have a medical condition or are pregnant.
Questions people ask
How is BMI calculated?
BMI = weight in kilograms ÷ height in metres squared. In pounds and inches it is 703 × weight ÷ height². For example, 70 kg at 1.75 m is 70 ÷ 3.0625 = 22.9.
What are the BMI categories?
For adults, the World Health Organization uses: under 18.5 underweight, 18.5 to 24.9 healthy weight, 25 to 29.9 overweight, and 30 or above obesity. Some countries use different cut-offs for certain populations, for example lower thresholds for people of Asian descent.
Is BMI accurate?
It is a quick screening measure, not a diagnosis. BMI cannot tell fat from muscle, so very muscular people can score as overweight. It also does not show where fat is stored. Waist measurement and a health check give a fuller picture.
Does it work for children and teens?
Not with these categories. For people under 18, BMI is compared with growth charts for their age and sex. Use the percentile tools from your national health service instead.
What is BMI Prime?
BMI Prime is your BMI divided by 25, the upper limit of the healthy range. A value below 1.0 means you are within the range, and above 1.0 means you are above it.