Is BMI useful if you exercise or have substantial muscle?
See why muscular people can have a high BMI and which additional measures provide better body-composition context.
BMI cannot distinguish muscle from fat. Because both contribute to body weight, a muscular athlete may fall into an overweight—or occasionally obesity—category despite having relatively low body fat.
That does not make the calculation wrong; it means the screening measure has limited specificity for that person. BMI can still offer a consistent weight-to-height reference and may be useful when viewed over time.
Add context with waist circumference, performance, blood pressure, laboratory results and a body-composition estimate. Skinfolds, bioelectrical impedance and tape-measure equations each have measurement error, while imaging methods are more precise but less accessible. Use the same method and conditions when tracking change.
Do not automatically dismiss a high BMI because you train. Muscle may explain some or much of it, but central fat and metabolic risk can still coexist. A clinician can interpret the complete picture when risk factors are present.
Compare the BMI calculator with the body fat percentage calculator for two different, imperfect perspectives.