What is BMI?
BMI stands for body mass index. It compares your weight to your height. The formula is your weight in kilograms divided by your height in meters, squared. Doctors use it as a quick first check of weight status for adults.
What your BMI means
These are the adult categories used by the CDC:
- Under 18.5: underweight
- 18.5 to under 25: healthy weight
- 25 to under 30: overweight
- 30 or higher: obesity
The limits of BMI
BMI is simple, and that is also its weak spot. It only looks at two numbers, so it misses a lot about your health.
- Muscle counts as weight. BMI can’t tell muscle from fat. Athletes and people who lift weights often have a BMI in the “overweight” range while being lean and healthy.
- It fits older adults less well. As we age, we tend to lose muscle and gain fat, even at the same weight. A 2014 review found that for adults 65 and older, a BMI a little over 25 was not linked to a higher risk of death. A BMI under 23 was.
- It doesn’t show where fat is. Fat around the belly carries more health risk than fat on the hips or thighs. A waist measurement can help here.
- It isn’t the same for every group. Some ethnic groups face more health risks at a lower BMI. BMI is also not used for children or during pregnancy.
What to do next
Use your BMI as one piece of the picture, not the whole story. If you want to change your weight, protein helps you keep muscle while you do. Try our protein calculator or find out your calorie needs with the TDEE calculator. Adults 50 and older can read our guide for adults 50+.
Talk to your doctor about what a healthy weight looks like for you.