Use the right calculation
Enter a recent weight and measured height into an adult calculator, checking the units. BMI does not directly measure body fat or where it is carried. Pregnancy, age, muscle mass and some medical circumstances affect interpretation. A very muscular person and somebody with little muscle can have the same BMI for different reasons.
Thresholds need context
For many adults, BMI 25 to 29.9 is classified as overweight and 30 or above as obesity. Risk can occur at lower BMI in some ethnic groups, so an adult calculator may ask about ethnicity. These are assessment categories, not a verdict about one person or automatic eligibility for a particular medicine.
Look beyond the single number
- Ask about waist measurement and waist-to-height ratio where appropriate; these add information about central fat.
- Consider blood pressure, cholesterol, blood glucose, family history and symptoms with a clinician.
- Notice practical progress too: what you can do, how you feel and whether a plan is sustainable.
- If you are older, frail or losing weight unintentionally, ask for individual assessment rather than trying to reach a calculator category.
Make it useful without making it your identity
Write down the question behind the calculation. Perhaps you want to understand a GP result, compare treatment options or decide whether to book a health check. Take that question to the appropriate professional. Recalculating BMI every day is unlikely to answer it. If weighing or measuring is causing distress, you can seek support without supplying a perfect set of numbers first.