How to lose or gain weight safely using BMI as a guide
Learn how to use BMI as a starting point when considering a change in weight, without treating it as a diagnosis.
BMI can help you place your weight in context, but it should not dictate a target on its own. For most adults, a BMI below 18.5 is classified as underweight, 18.5–24.9 as healthy weight, 25.0–29.9 as overweight and 30.0 or above as obesity.
If your result is below the reference range, a gradual increase in energy intake may be appropriate. Prioritize regular meals, nutrient-dense foods and strength training when suitable. Unintentional weight loss, digestive symptoms or a very low BMI warrant professional assessment.
If your BMI is above the range, modest, sustainable changes are usually more useful than an aggressive diet. Review portions, food quality, daily movement, sleep and your estimated energy needs. Track trends over several weeks rather than reacting to a single weigh-in.
A BMI within the reference range does not automatically mean that you need to maintain the exact same weight. Muscle mass, waist measurement, medical history, medications and how you feel all matter.
Use the BMI calculator as a screening step. If you plan a substantial weight change, are pregnant, are under 20, have an eating disorder history or live with a medical condition, seek individualized advice.