Understanding BMI: what the numbers actually mean
By New Start Slimming Clinic
If you've ever looked into weight management, you'll have come across BMI - body mass index. It's one of the first things we check at your consultation, alongside your blood pressure and a full medical history. But what does the number actually tell you?
What BMI measures
BMI is a simple calculation using your height and weight. It gives a single number that places you in a broad category - from underweight through to a healthy range, overweight, and obese. Because it's quick and consistent, it's widely used as a starting point by clinicians across the NHS and private practice alike.
As a general guide, the standard adult ranges are:
- Below 18.5 - underweight
- 18.5 to 24.9 - healthy weight
- 25 to 29.9 - overweight
- 30 and above - obese
Why it's only a starting point
BMI is useful, but it's a blunt instrument. It doesn't distinguish between muscle and fat, so a very muscular person can have a high BMI without excess body fat. It also doesn't tell you where you carry weight - and weight carried around the middle carries more health risk than weight elsewhere.
That's exactly why we never treat BMI as the whole picture. At New Start, the number is one input among many. We look at your overall health, any weight-related conditions, your medical history and your goals before discussing whether treatment is appropriate for you.
What matters more than the number
Two people with the same BMI can be in very different situations. What we're really interested in is your health and how we can help you improve it - sustainably, and safely. A single number never decides that; a proper assessment does.
If you're wondering where you stand and what your options might be, the best first step is a consultation with one of our GMC-registered doctors.