BMI, or body mass index, is weight divided by height squared - a rough screening figure that takes no account of muscle, frame or body composition. BMI against the CDC’s actual adult categories, and daily calories from the clinically validated Mifflin–St Jeor equation - with the limits of both stated plainly, not buried.
BMI is weight divided by height squared (kg/m²), and the CDC's adult categories are: under 18.5 underweight, 18.5–24.9 healthy range, 25–29.9 overweight, 30 and above obesity. It's a screening tool - useful at the population level, but it can't tell muscle from fat, so a muscular athlete can register "overweight" while carrying very little body fat. Treat the category as a prompt for a conversation with a doctor, not a diagnosis.
The daily calorie figure starts from your basal metabolic rate using the Mifflin-St Jeor equation - published in the American Journal of Clinical Nutrition (Mifflin et al., 1990) and found in a 2005 systematic review to predict resting metabolic rate within 10% of measured values more often than any competing formula. For men: 10×weight + 6.25×height − 5×age + 5. For women: the same, with −161 instead of +5. That resting figure is then multiplied by a standard activity factor (1.2 sedentary up to 1.9 very active) to estimate total daily energy expenditure - the calories that roughly maintain your current weight.
These are population formulas applied to an individual - real metabolic rates vary, and the equation is least accurate at very high or very low body weights. The activity multiplier is also famously easy to overestimate: training hard 5 days a week with a desk job is closer to "moderate" than "very active." If precision matters for a medical or athletic goal, measured approaches (like indirect calorimetry through a clinic) beat any formula.
BMI is weight in kilograms divided by height in metres squared. Someone 1.75 m tall weighing 70 kg has a BMI of 22.9.
It is a rough screening tool, not a measure of health. It takes no account of muscle mass, frame size or body composition, so athletes often register as overweight while the figure can miss genuine risk in others.