How this calculator works
Body mass index compresses height and weight into one comparable number. It is fast, inexpensive and useful for population screening, which is why clinicians and public-health systems still use it.
It does not separate fat from muscle, show where fat is stored, or account for pregnancy and some body-type differences. A muscular athlete and a sedentary person can share a BMI while having very different body composition.
BMI = weight in kilograms ÷ height in metres². Adult categories used here are: below 18.5, 18.5–24.9, 25.0–29.9 and 30 or above.
How to use the result
Use BMI as one signal alongside waist measurement, blood pressure, laboratory results, fitness, symptoms and medical history. A category is not a diagnosis and should not be used to judge health or worth.
The reference weight interval shown is simply the weight span that produces BMI 18.5–24.9 at the entered height. It is not a personalised target, and a clinician may use different priorities.
Get a more reliable result
Measure weight on a level scale and height without shoes, heels together and eyes facing forward. Use the same scale and similar conditions when following change. BMI is a population screening ratio; record waist or body-composition context alongside it when muscularity, age or fat distribution may change the interpretation.
Common errors that change the answer
- Entering centimetres as metres or mixing pounds with kilograms.
- Using BMI alone to label a muscular athlete or an older adult with low muscle mass.
- Applying adult categories during pregnancy or to children, who require different interpretation.
What to do next
- Measure height without shoes and weight under similar conditions.
- Pair BMI with waist-to-height ratio for another view of central fat.
- Discuss an unexpected or rapidly changing result with a health professional.
Guides that support this calculator
Frequently asked questions
Is BMI accurate for athletes?
It calculates correctly, but interpretation can be misleading when high muscle mass raises body weight. Add waist and body-composition context.
Does BMI work during pregnancy?
It is not interpreted in the usual way during pregnancy. Use pregnancy-specific guidance from your care team.
Is BMI a diagnosis?
No. It is a screening measure that helps decide whether more context or assessment may be useful.