BMI Calculator for Kids

Early Childhood (Ages 2-5)

Young children transition from baby fat to leaner bodies. BMI naturally decreases during these years as children stretch out and become more active. This is normal and expected. Growth occurs in spurts rather than steadily, so weight may fluctuate.

• Height increases about 3-4 inches per year
• Weight gain averages 4-5 pounds per year
• Body proportions change as legs grow longer
• Appetite may vary considerably day to day
• Activity levels increase significantly

Middle Childhood (Ages 6-9)

Children grow steadily and develop strength and coordination. BMI typically remains relatively stable during these years, though individual variation is normal. Some children are naturally leaner while others are stockier.

• Height increases 2-3 inches per year
• Weight gain averages 5-7 pounds annually
• Muscle development increases, especially with activity
• Baby teeth lost and permanent teeth emerge
• Growth is generally steady without major spurts

Pre-Puberty (Ages 10-12)

Children approach puberty, and BMI may begin increasing as the body prepares for adolescent growth. Girls typically enter puberty earlier than boys and may show weight gain before height spurts.

• Growth patterns become more variable between children
• Some children begin puberty-related changes
• Weight gain may precede height growth spurts
• Body composition starts shifting
• Appetite often increases noticeably

Why does my child's BMI percentile change?

Children's BMI percentiles naturally fluctuate as they grow. Height spurts, seasonal activity changes, and developmental stages all affect weight and BMI. Small percentile shifts (10-15 points) are usually normal. Large or rapid changes, or percentiles consistently at extremes (<5th or >95th) warrant discussion with a pediatrician.

Should I tell my child their BMI percentile?

Generally, no. Young children don't need to know specific BMI numbers or percentiles, as this can create unhealthy focus on weight. Instead, emphasize healthy behaviors like eating nutritious foods, being active, and feeling strong. If discussing health with older children, focus on habits and wellness rather than numbers. Let healthcare providers handle medical discussions.

My child looks healthy but has high BMI percentile. Why?

Some children are naturally stockier or more muscular, especially if they're very active in sports. BMI doesn't distinguish muscle from fat. However, if BMI percentile is above 85th persistently, it's worth discussing with a pediatrician who can assess body composition, family history, growth trends, and overall health. Sometimes children who appear healthy do have excess body fat that poses health risks.

How often should I check my child's BMI?

BMI should be calculated at routine well-child checkups (typically annually for school-age children). More frequent checking at home is generally unnecessary and may create unhealthy focus on weight. If your pediatrician has concerns, they may recommend more frequent monitoring. Otherwise, annual measurements are sufficient to track growth patterns.

What if my child refuses to eat vegetables or healthy foods?

Food preferences are normal, but parents control what foods are available. Offer variety, make healthy foods appealing, involve children in meal preparation, and model healthy eating yourself. Don't force foods, but don't provide alternatives if they refuse healthy meals. Children may need 10-15 exposures to a new food before accepting it. Avoid battles over food, which can worsen the situation.

Can children diet to lose weight?

Children should never be put on restrictive diets without medical supervision. Growing bodies need adequate nutrition for development. Instead of dieting, focus on family-wide healthy eating patterns, appropriate portion sizes, reducing processed foods and sugary drinks, and increasing activity. If a pediatrician recommends weight management, they'll provide guidance that ensures continued healthy growth.

Why are there different charts for boys and girls?

Even in childhood, boys and girls have different body composition and growth patterns. Girls naturally have slightly higher body fat percentages, and they typically begin puberty-related weight gain earlier than boys. Boys tend to develop more muscle mass as they grow. Using gender-specific charts ensures accurate percentile interpretation that accounts for these normal biological differences.

What role does genetics play in child BMI?

Genetics significantly influences body type, but genes aren't destiny. Children with overweight parents have higher risk of high BMI, but healthy lifestyle choices make a huge difference. Family eating patterns, activity levels, and habits are often more influential than genetics alone. Creating a healthy home environment can help children maintain healthy weight regardless of genetic predisposition.