Your BMI, or Body Mass Index, tells you how much fat there is in your body. An accurate BMI reading is a great way to tell whether or not you’re at a healthy weight. If your BMI is too high you are at a greater risk of weight-related health problems like heart disease, stroke and diabetes. Maintaining a healthy BMI is one of many ways to stay healthy and reduce your risk of future problems.

To calculate your BMI, you simply need to know your weight in kilograms and your height in meters. A healthy BMI range for men and women is between 18.5 and 25. Below 18.5 is considered underweight, 25 to 30 is overweight, and over 30 is considered obese.

You should monitor your BMI regularly if you think you weight is changing (or needs changing). That means if you gain weight OR if you lose weight. While it doesn’t garner nearly as much attention, a BMI that is too low is just as dangerous as one that is too high. If your BMI is below 18.5, you should alter your habits to gain weight in a healthy manner. A doctor can help you come up with a weight gain plan just as they would for weight loss.

While you may be an adult legally when you turn eighteen, BMI calculations don’t consider you an adult until you’re twenty. Women under age twenty can calculate their BMI in the same way as adults, but the cut-offs for a healthy range are different and vary by age. If you’re nineteen or younger, you should check age/weight ratio charts to determine if you fall in the healthy range. A BMI less that 5% of other women your age is considered underweight, between 5 and 85 percent is healthy, 85 to 95 percent is overweight, and above 95% is obese.

Just because your BMI doesn’t fall into the healthy range doesn’t mean you need to lose gain weight. If you are older, or if you are an athlete or just very muscular, your BMI may not be accurate. This is because BMI is a general tool developed for men and women aged twenty and above, and isn’t specific to age, sex, or body type. If your BMI is high or low, you should consider getting a more accurate reading of body fat percentage from your doctor. Also, if you eat healthy and exercise regularly, you are probably less likely to have health issues than someone with the same BMI and a poor lifestyle.

If your BMI is not in the healthy range, your best course of action is to visit your doctor. The can give you a healthy weight loss or weight gain plan that is right for you.