BMI has limitations. It may overestimate body fat in athletes and muscular individuals, and underestimate it in older persons who have lost muscle mass. It also doesn't account for fat distribution. It's best used as one of several health indicators.

Higher BMI categories are associated with increased risk of conditions like heart disease, type 2 diabetes, and certain cancers. However, BMI alone doesn't determine health - factors like fitness level, diet quality, and genetics also play important roles.

If you're actively managing your weight, checking monthly can help track progress. Otherwise, checking a few times per year or at annual checkups is usually sufficient. Daily fluctuations in weight are normal and not meaningful.

For children and teens (ages 2-19), BMI is calculated the same way but interpreted differently using age and sex-specific percentiles. This calculator is designed for adults (20+). Consult a pediatrician for children's BMI assessment.

Muscle weighs more than fat. If you have significant muscle mass from regular exercise, your BMI may be higher than expected. This is why BMI can be misleading for athletes. Consider body fat percentage for a more accurate picture.

If your BMI indicates underweight, overweight, or obesity, consider consulting a healthcare provider. They can assess your overall health, consider factors BMI doesn't capture, and recommend appropriate steps if needed.