Understanding BMI and Daily Calorie Needs
BMI and TDEE are two of the most useful starting numbers for any fitness or weight goal. One estimates whether your weight is in a healthy range; the other estimates how many calories you burn in a day. Used together, they help you set realistic targets. Neither is a diagnosis — they are guides, not medical advice.
What BMI tells you
Body Mass Index relates your weight to your height: BMI = weight (kg) ÷ height (m)² (or 703 × lb ÷ in² in imperial). It sorts into broad categories — under 18.5 underweight, 18.5–24.9 normal, 25–29.9 overweight, 30+ obese. Calculate yours with the BMI calculator.
BMI's limitations
BMI does not distinguish muscle from fat, so athletes can read as "overweight" despite low body fat. It also ignores age, sex and fat distribution. Treat it as a population-level screen, not a verdict on an individual.
What TDEE tells you
Total Daily Energy Expenditure is the calories you burn per day, including activity. It starts from your BMR (basal metabolic rate) using the Mifflin–St Jeor formula, then multiplies by an activity factor (1.2 sedentary up to 1.9 very active). The TDEE calculator also suggests calorie targets and a macro split.
Using them together
- To lose weight — eat below your TDEE (a moderate deficit of ~10–20%).
- To maintain — eat at your TDEE.
- To gain — eat above it, paired with strength training.
BMI helps set the direction; TDEE sets the daily number to hit it. As inputs like age change your BMR over time, recompute periodically — the age calculator gives an exact age, and if you track running, the running pace calculator helps plan training that adds to your daily burn.
For significant changes to diet or exercise, consult a qualified professional.