How to read your BMI score

BMI stands for Body Mass Index. It is a number that compares your weight to your height. Doctors and health apps have used BMI since the 1970s as a quick way to estimate whether someone falls into a healthy weight range. Your BMI is a single number, usually between 15 and 40. The standard adult chart from the Centers for Disease Control says: under 18.5 is underweight, 18.5 to 24.9 is healthy weight, 25.0 to 29.9 is overweight, and 30.0 or higher is obese. Your phone, smart scale, or doctor's office can calculate BMI for you in seconds. To work it out by hand, take your weight in pounds, multiply by 703, then divide by your height in inches squared. For example, a person who weighs 160 pounds and stands 5 feet 6 inches tall (66 inches) has a BMI of about 25.8. Keep in mind, BMI is a rough screening tool, not a diagnosis. It does not measure muscle, bone density, or where fat sits on your body. A retired athlete with strong muscles may show a high BMI but still be very healthy. An older adult who has lost muscle may show a normal BMI while carrying too much belly fat. For people 65 and older, many doctors prefer a slightly higher healthy range, around 23 to 30, because a small cushion of weight protects against illness and falls. Use BMI as one signal among several, alongside blood pressure, cholesterol, waist size, and how you feel day to day. If your BMI changes by more than two points in either direction within six months, mention it at your next checkup. Never start a weight loss or gain plan from BMI alone — talk with your clinician first.