Free BMI Calculator – Check Your Body Mass Index Instantly

What is Body Mass Index (BMI)?

Body Mass Index (BMI) is a value derived from the mass (weight) and height of a person. The BMI is defined as the body mass divided by the square of the body height, and is expressed in units of kg/m², resulting from mass in kilograms and height in metres.

The BMI is a convenient rule of thumb used to broadly categorize a person as underweight, normal weight, overweight, or obese based on tissue mass (muscle, fat, and bone) and height. Major adult BMI classifications are underweight (under 18.5 kg/m²), normal weight (18.5 to 24.9), overweight (25 to 29.9), and obese (30 or more).

BMIs under 20 and over 25 have been associated with higher all-causes mortality, with the risk increasing with distance from the 20–25 range.

How to Use This BMI Calculator

Our free BMI calculator is designed to be simple and user-friendly. Follow these steps to calculate your Body Mass Index:

1. Enter your age in years (optional but recommended for accurate results)
2. Select your gender (required for children and teens)
3. Choose your preferred height unit (centimeters or feet/inches)
4. Enter your height in the selected unit
5. Choose your preferred weight unit (kilograms or pounds)
6. Enter your weight in the selected unit
7. Click the "Calculate BMI" button to get your results

The calculator will instantly display your BMI value, category, and personalized health insights. For children and teens, the calculator will also show the BMI percentile, which compares their BMI to others of the same age and gender.

BMI Ranges: What Your Score Means

Understanding your BMI result is crucial for assessing your health status. Here are the standard BMI categories and what they mean:

For children and teens, BMI is interpreted differently using percentiles that account for age and gender. The percentile indicates how a child's BMI compares to other children of the same age and gender.

BMI Categories for Adults

The standard weight status categories associated with BMI ranges for adults are shown in the following table. These categories are the same for men and women of all body types and ages.

BMI chart for adults based on WHO data

How is BMI interpreted for adults?

For adults 20 years old and older, BMI is interpreted using standard weight status categories. These categories are the same for men and women of all body types and ages.

The standard weight status categories associated with BMI ranges for adults are shown in the table above.

BMI Categories for Children and Teens

BMI is interpreted differently for children and teens even though it is calculated using the same formula as adult BMI. Children body composition varies as they age and varies between boys and girls. Therefore, BMI levels among children and teens need to be expressed relative to other children of the same age and sex.

BMI categories for children and teens (2-20 years) by CDC

How is BMI interpreted for children and teens?

For children and teens, BMI is age- and sex-specific and is often referred to as BMI-for-age. A child weight status is determined using an age- and sex-specific percentile for BMI rather than the BMI categories used for adults. This is because children body composition varies as they age and varies between boys and girls.

The percentiles are then used to determine the weight categories:

• Underweight: BMI < 5th percentile
• Healthy weight: BMI 5th percentile to < 85th percentile
• Overweight: BMI 85th percentile to < 95th percentile
• Obese: BMI ≥ 95th percentile

Health Risks Associated with High BMI

People who are overweight or obese are at higher risk for chronic conditions such as high blood pressure, diabetes, and high cholesterol. Regardless of your BMI, knowledge of your waist circumference is important because it provides additional information on your health risks.

Risks Associated with Obesity

Obesity is a serious health concern that increases the risk of numerous health problems. Some of the health risks associated with obesity include:

• Type 2 Diabetes: Obesity is a major risk factor for type 2 diabetes. Excess body fat can cause insulin resistance, leading to high blood sugar levels.
• Heart Disease: Obesity increases the risk of heart disease and stroke. It can lead to high blood pressure, high cholesterol, and other cardiovascular problems.
• Certain Types of Cancer: Obesity has been linked to an increased risk of several types of cancer, including breast, colon, endometrial, and kidney cancer.
• Sleep Apnea: People who are obese are more likely to have sleep apnea, a serious sleep disorder where breathing repeatedly stops and starts during sleep.
• Osteoarthritis: Excess weight puts additional pressure on joints, particularly the knees and hips, leading to osteoarthritis.
• Fatty Liver Disease: Obesity is a leading cause of nonalcoholic fatty liver disease (NAFLD), a condition where fat builds up in the liver.
• Kidney Disease: Obesity increases the risk of chronic kidney disease and kidney stones.
• Pregnancy Problems: Obesity during pregnancy can increase the risk of complications for both the mother and the baby.

Risks Associated with Being Underweight

While much attention is given to the health risks of being overweight or obese, being underweight can also pose health risks. Some of the health risks associated with being underweight include:

• Malnutrition: Being underweight can be a sign of malnutrition, which can lead to deficiencies in essential vitamins and minerals.
• Weakened Immune System: Malnutrition can weaken the immune system, making it harder for the body to fight off infections.
• Osteoporosis: Being underweight increases the risk of osteoporosis, a condition where bones become weak and brittle.
• Anemia: Underweight individuals are at higher risk for anemia, a condition characterized by a lack of healthy red blood cells.
• Fertility Issues: Being underweight can disrupt hormonal balance and lead to fertility problems in both men and women.
• Growth and Development Issues: In children and adolescents, being underweight can affect growth and development.

Risk Level by BMI Category

How to Maintain a Healthy BMI

Maintaining a healthy BMI is essential for overall health and well-being. It involves a combination of healthy eating, regular physical activity, and lifestyle changes. Here are some tips to help you maintain a healthy BMI:

Healthy Eating Habits

• Eat a Balanced Diet: Include a variety of foods from all food groups: fruits, vegetables, grains, protein foods, and dairy or fortified soy alternatives.
• Portion Control: Be mindful of portion sizes to avoid overeating. Use smaller plates and bowls to help control portions.
• Limit Processed Foods: Reduce intake of processed foods, which are often high in added sugars, sodium, and unhealthy fats.
• Stay Hydrated: Drink plenty of water throughout the day. Sometimes thirst can be mistaken for hunger.
• Eat Regular Meals: Do not skip meals, especially breakfast. Eating regular meals helps maintain energy levels and prevents overeating later.
• Limit Added Sugars: Reduce consumption of sugary drinks, desserts, and foods with added sugars.
• Choose Healthy Fats: Opt for unsaturated fats found in foods like avocados, nuts, seeds, and olive oil instead of saturated and trans fats.

Regular Physical Activity

• Aim for 150 Minutes of Moderate Activity: Engage in at least 150 minutes of moderate-intensity aerobic activity or 75 minutes of vigorous-intensity aerobic activity per week.
• Include Strength Training: Incorporate muscle-strengthening activities at least two days per week.
• Find Activities You Enjoy: Choose physical activities that you enjoy to make exercise a sustainable part of your routine.
• Increase Daily Movement: Look for opportunities to be more active throughout the day, such as taking the stairs instead of the elevator or walking instead of driving for short distances.
• Set Realistic Goals: Start with small, achievable goals and gradually increase the intensity and duration of your workouts.

Lifestyle Changes

• Get Adequate Sleep: Aim for 7-9 hours of quality sleep per night. Lack of sleep can disrupt hormones that regulate appetite.
• Manage Stress: Chronic stress can lead to emotional eating and weight gain. Practice stress-reduction techniques like meditation, deep breathing, or yoga.
• Monitor Your Progress: Regularly check your BMI and waist circumference to track your progress.
• Seek Support: Consider joining a weight management program or working with a registered dietitian or personal trainer for guidance and support.
• Be Patient: Healthy weight loss and maintenance take time. Aim for gradual changes rather than quick fixes.

BMI Limitations

While BMI is a useful tool for assessing weight status at a population level, it has limitations when applied to individuals. It is important to understand these limitations when interpreting your BMI results.

Limitations of BMI

• Does not Measure Body Fat Directly: BMI is a calculation based on height and weight and does not directly measure body fat or body composition.
• Does not Account for Muscle Mass: Individuals with high muscle mass, such as athletes, may have a high BMI but low body fat.
• Does not Consider Fat Distribution: BMI does not account for where fat is stored in the body. Abdominal fat is more strongly associated with health risks than fat stored in other areas.
• May Not Be Appropriate for All Ethnic Groups: The standard BMI categories may not be appropriate for all ethnic groups. For example, people of Asian descent may have an increased risk of health problems at a lower BMI.
• Does not Account for Age and Gender Differences: While BMI-for-age percentiles are used for children and teens, the standard BMI categories do not account for age and gender differences in adults.
• Does not Consider Overall Health: BMI does not provide information about overall health, diet, physical activity levels, or other lifestyle factors that influence health.

Alternative Measures

Because of these limitations, healthcare providers may use other measures in addition to BMI to assess health risks, including:

• Waist Circumference: Measures abdominal fat, which is a better predictor of health risks than BMI alone.
• Waist-to-Hip Ratio: Compares the circumference of the waist to that of the hips.
• Body Fat Percentage: Measures the proportion of fat to lean body mass.
• Blood Pressure: Measures the force of blood against the walls of the arteries.
• Blood Tests: Can measure cholesterol levels, blood sugar levels, and other indicators of health.