If you're left scratching your head every time you encounter the phrase body mass index (BMI) in a nutrition or fitness article, don't worry. BMI is a simple formula that physicians, nurses, dietitians and you can use to evaluate your health.

BMI is an estimate of total body fat based on your height and weight. It's important to know your BMI because excess body fat can put you at risk for health problems such as cancer, cardiovascular disease and diabetes. To calculate your BMI yourself, use this formula: [ weight in pounds ÷ height in inches ÷ height in inches] x 703.

Once you've determined your BMI, you can determine whether you're in the underweight, normal weight, overweight or obese category. Here are the guidelines:

• Underweight: BMI of less than 18.5
• Normal Weight: BMI of 18.5-24.9
• Overweight: BMI of 25.0 to 29.9
• Obese: BMI of 30.0 or more

Your doctor or health care provider will take more than BMI into account when evaluating your health - your waist circumference and other lifestyle issues (such as a history of heart disease or your smoking status) may also affect your risk of certain health conditions. For people who are athletes and who have muscular builds, the BMI may overestimate total body fat, since muscle weighs more than fat. And in seniors or those who have lost muscle mass, the BMI may underestimate body fat.

Related information Lifeclinic BMI calculator

Sources:  National Heart, Lung, and Blood Institute: http://nhlbisupport.com/bmi/; Centers for Disease Control and Prevention: http://www.cdc.gov/nccdphp/dnpa/bmi/calc-bmi.htm; http://www.cdc.gov/nccdphp/dnpa/bmi/index.htm