Your body mass index, or BMI, is a marker health care providers use to determine if you're at or near a healthy weight. The exact equation to figure your BMI is complicated but boils down to a basic relationship between your height and your weight. Unless you are a child or teen, age doesn't factor into what is considered healthy for your BMI. A healthy BMI for a 25-year-old woman is the same as for a woman of any age -- between 18.5 and 24.9.
How Reliable Is BMI?
Although the Centers for Disease Control and Prevention asserts that BMI is a decent measure of body fatness for most people, the measure isn't perfect. If you fall outside the normal range, follow up with your health care provider. Anyone who is particularly athletic or has a muscular build may appear fat according to the calculations when, in fact, their weight and size is healthy.