Not perfectly — BMI can’t tell muscle from fat, so it tends to overstate body fat in muscular or athletic people and understate it in older adults who’ve lost muscle mass. Treat it as a rough screening number, not a diagnosis.

Below 18.5 is classified as underweight, 18.5 to 24.9 as normal weight, 25 to 29.9 as overweight, and 30 or above as obesity.

If your number falls outside the normal range, or you simply have questions about your weight or health more broadly, a healthcare provider can look at the full picture in a way a single number never can.