Body mass index (BMI) or bmi calculator is a health metric used to gauge a person’s weight category quickly, as it’s a simple calculation of body fat relative to weight and height.

While BMI has its limitations—and should not be the only metric considered when determining your weight class—it’s a fast and accessible tool that can help you better understand whether you carry excess body fat, which can put you at risk for health complications ranging from type 2 diabetes to high blood pressure.

Body mass index, or BMI, is a quick and inexpensive measurement of your body fat in relation to your weight and height. It’s often used as a screening tool for weight class categories, but it’s only moderately correlated with direct measurements of body fat, according to the Centers for Disease Control and Prevention (CDC).

In fact, even if two people have the same BMI, their body fat percentages may differ because a high BMI can indicate not only high levels of body fat, but also high levels of lean body mass, which is composed of muscle and bone.

What Are the Limitations to Using bmi calculator for Body Fat Calculation?

As noted above, BMI is considered an imperfect measurement of body fat, as it doesn’t measure body fat directly. Additionally, BMI charts don’t take age, gender, race and ethnicity into account (with the exception of age and sex for children and teens), which can also impact your body fat or muscle. Indeed, experts note other factors you should take into consideration when determining your weight category include the location of fat, total muscle mass, age and gender. When calculating your BMI, keep these limitations in mind.

What Is a Healthy BMI?

A healthy BMI for an adult is 18.5 to 24.9, according to the CDC. A BMI of less than 18.5 is considered underweight while a BMI of 25.0 to 29.9 is considered overweight. A BMI higher than 30.0 is considered obese.

It’s important to mention that while BMI is a screening tool, it’s not a true diagnostic measurement of body fat or the health of an individual.

How Much Should You Walk Daily According to BMI?

If an individual has a higher BMI and is looking to add more activity to their routine, 30 minutes of walking each day, or about 3,000 to 5,000 steps (1.5 to 3 miles), is recommended. This advice also pertains to those with a lower BMI who are just starting out with adding more exercise to their day.

For a person with a lower BMI who is already active, 60 to 90 minutes of walking is advisable. This equates to about 10,000 steps (or 5 to 7 miles) for most people. The average American should aim to fit in about 30 minutes of exercise per day.