Calculate your Body Mass Index and daily calorie needs with these free health tools.
| Category | BMI Range |
|---|---|
| Underweight | Below 18.5 |
| Normal weight | 18.5 - 24.9 |
| Overweight | 25.0 - 29.9 |
| Obese | 30.0 and above |
This tool combines two essential health calculators. The BMI Calculator computes your Body Mass Index -- a screening metric that categorizes your weight relative to your height. The Calorie Calculator estimates how many calories you need each day to maintain, lose, or gain weight using the Mifflin-St Jeor equation, one of the most accurate methods available for estimating resting metabolic rate.
BMI is a useful population-level screening tool, but it has important limitations. It does not distinguish between muscle and fat, so muscular athletes often register as "overweight" despite having low body fat. It also does not account for bone density, age, or where you carry your weight. Waist circumference and body fat percentage are better indicators of health risk for individuals who fall outside the typical range. Use BMI as one data point, not the sole measure of your health.
BMI tends to overestimate body fat in muscular individuals because it cannot differentiate between muscle mass and fat mass. A bodybuilder with 10% body fat could have a BMI over 30 and be classified as "obese" by the scale. If you carry significant muscle, consider using body fat percentage or waist-to-hip ratio instead.
Research suggests that a slightly higher BMI (23-27) may be protective for adults over 65, as being underweight in older age is associated with higher mortality risk. The standard 18.5-24.9 "normal" range was developed primarily from younger adult populations. Consult your doctor for age-appropriate guidance.
A deficit of 500 calories per day below your maintenance level leads to roughly one pound of weight loss per week, which is considered a safe and sustainable rate. Avoid going below 1,200 calories per day for women or 1,500 for men without medical supervision, as very low calorie intake can cause nutrient deficiencies and metabolic slowdown.
BMI for children and teens is calculated the same way but interpreted differently. Pediatric BMI uses age- and sex-specific percentiles rather than fixed category cutoffs, because body composition changes significantly during growth. This calculator is designed for adults aged 18 and older.
Your body burns calories not just at rest but through daily movement and exercise. The activity multiplier adjusts your base metabolic rate to reflect your total daily energy expenditure. Selecting the wrong activity level is the most common source of error, so choose the option that honestly reflects your average week.