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BMI Chart for Children and Teens (Ages 2–20)

The Centers for Disease Control and Prevention (CDC) provides BMI-for-age percentile growth charts to assess children’s and teens’ weight categories.

• Chart for Boys

• Chart for Girls

Health Risks Linked to Being Overweight

Carrying excess weight is associated with several serious health conditions and diseases. According to the CDC, the potential risks include:

• High blood pressure (hypertension)

• Unhealthy cholesterol levels: higher LDL (“bad” cholesterol), lower HDL (“good” cholesterol), and elevated triglycerides

• Type 2 diabetes

• Heart disease (coronary heart disease)

• Stroke

• Gallbladder issues

• Osteoarthritis (joint damage caused by cartilage wear)

• Sleep apnea and other breathing difficulties

• Certain types of cancer (such as breast, colon, kidney, liver, gallbladder, and endometrial)

• Reduced quality of life

• Mental health challenges, including anxiety and depression

• Frequent body aches and limited mobility

• Increased risk of premature death compared to individuals with a healthy BMI

In general, maintaining a BMI below 25 kg/m² is recommended for adults. However, it’s always best to consult with a healthcare professional to determine whether lifestyle changes are necessary for improving overall health.

Risks Associated with Being Underweight

Just like being overweight, having a BMI that falls below the healthy range can also pose serious health concerns. Common risks of being underweight include:

• Malnutrition and vitamin deficiencies – Lack of proper nutrients can lead to fatigue, weakness, and anemia (reduced ability of blood to carry oxygen).

• Bone health issues (Osteoporosis) – Lower body weight increases the risk of bone fragility and fractures.

• Weakened immune system – Making the body more vulnerable to infections and slower recovery from illnesses.

• Growth and development delays – Particularly in children and teens, where proper nutrition is crucial for physical and cognitive development.

• Reproductive and hormonal problems – Women may experience irregular menstrual cycles, hormonal imbalances, or even increased risk of miscarriage during early pregnancy.

• Surgical complications – Higher risk of poor wound healing and complications after medical procedures.

• Higher risk of mortality – Studies show that being underweight can be linked to reduced life expectancy, similar to obesity.

In some cases, being underweight may indicate an underlying condition such as eating disorders (like anorexia nervosa) or other medical issues. If you or someone you know is underweight without a clear reason, it’s important to consult a doctor for proper evaluation and guidance.

Limitations of BMI

While BMI is one of the most commonly used indicators for assessing healthy weight, it does have certain limitations. It should not be seen as a perfect measure, but rather as a general guideline. The main issue with BMI is that it does not consider body composition—meaning it cannot distinguish between muscle, fat, and bone mass. Because of this, BMI should ideally be combined with other health assessments for a more accurate picture of overall health.

In Adults:

• Does not measure body fat directly – BMI reflects excess weight but not excess fat, which means two people with the same BMI may have very different body compositions.

• Age, sex, and ethnicity matter – Older adults often carry more body fat than younger adults at the same BMI, and women generally have more body fat than men at equivalent BMI levels.

• Activity level plays a role – A person with a sedentary lifestyle may have more fat even if their BMI is within a “healthy” range, while an active individual with higher muscle mass may appear “overweight” according to BMI, even though they are healthy.

• Athletes and bodybuilders – Since muscle weighs more than fat, muscular individuals may fall into the “overweight” or even “obese” BMI categories, despite being in excellent physical condition.

In short, BMI is a useful screening tool, but not a definitive measure of health. Other factors such as diet, activity level, body fat percentage, and medical history should also be considered when evaluating overall well-being.

BMI in Children and Adolescents

The same limitations that apply to adults also affect the accuracy of BMI in children and teenagers. Factors such as height, growth stage, and level of sexual maturity can influence both BMI and body fat levels.

• For obese children, BMI tends to be a stronger indicator of excess body fat.

• For overweight children, BMI may not always be reliable since a higher BMI could come from either increased fat or lean body mass (muscle, bone, water, organs, etc.).

• In thin children, differences in BMI may also be linked to fat-free mass rather than actual body fat.

Despite these limitations, studies show that BMI is a fairly accurate reflection of body fat for 90–95% of the population. When combined with other health assessments, it can be a useful tool to evaluate whether a child or adolescent is within a healthy weight range.

BMI Formula

BMI can be calculated using two different systems: the US customary system (USC) and the International System of Units (SI).

Example: For a person who is 5’10” tall and weighs 160 pounds.

USC Units:

BMI formula:

BMI = (703 × weight (lbs)) / height (in)²

Example:

BMI = (703 × 160) / 70² = 23.0

SI (Metric) Units:

BMI formula:

BMI = weight (kg) / height (m)²

Example:

BMI = 72.57 / (1.778)² = 23.0

This shows that BMI produces consistent results regardless of which system is used.

BMI Prime

BMI Prime is a quick way to compare a person’s Body Mass Index (BMI) with the highest value that’s still considered “normal.” Health organizations like the WHO and CDC usually set this upper healthy limit at 25 kg/m², though in some countries (especially in Asia) this standard may be slightly lower.

The formula is simple:

BMI Prime formula:

BMI Prime = BMI / 25

Example:

BMI Prime = 23.0 / 25 = 0.92​

Since it’s a ratio of two BMI values, BMI Prime has no units—it’s just a number.

• A BMI Prime below 0.74 means underweight.

• A BMI Prime between 0.74 and 1 is considered normal.

• A BMI Prime above 1 indicates overweight.

• A BMI Prime greater than 1.2 is classified as obese.

BMI Prime Classification Table

Why Use BMI Prime?

BMI Prime makes it easier to see how far someone’s weight is from the “normal” limit. It’s also useful when comparing people from different regions where the definition of a healthy BMI may vary.