As a key indicator of fat as a percentage of your overall weight, your Body Mass Index (BMI) is an invaluable tool for health and wellness.

The American Academy of Nutrition and Dietetics has guidelines for calculating your own BMI and tips for how BMI can help improve your health. While the Academy notes that BMI is just one of several factors that you and your doctor should consider when evaluating your health, the organization’s BMI calculator is a good place to start.

So why does BMI matter? As the Academy points out, anyone with either a very high or very low BMI faces greater health risks. However, even people with a healthy BMI are at risk if they smoke cigarettes, aren’t physically active, and eat food loaded with sugar and fats. Conversely, those who are overweight will have a lower health risk if they are physically active and have blood sugar, cholesterol and blood pressure levels that are within normal limits.

Regardless of your BMI, if you’re not happy with your fat-to-bodyweight ratio, more exercise can make a big difference.