A healthy BMI for adults is between 18.5 and 24.9. Below 18.5 is considered underweight, 25-29.9 is overweight, and 30 or above is classified as obese. These thresholds apply equally to all adults regardless of age.

BMI is a useful screening tool but has limitations. It does not distinguish between muscle and fat mass, so athletes or muscular individuals may have a high BMI despite low body fat. Waist circumference and body fat percentage provide additional context.

Checking BMI once every few months is sufficient for most adults. Significant changes in weight, diet, or exercise habits are good prompts to recalculate. Track the trend over time rather than focusing on a single reading.