Body Mass Index (BMI) for Children
Understanding BMI and what it means for your child's health and growth
🧮BMI Calculator
📐What is BMI?
Body Mass Index (BMI) is a calculation that uses height and weight to estimate body fat. It's a screening tool that helps doctors determine if a child is at a healthy weight for their height.
While BMI is the same calculation for adults and children, it's interpreted very differently for kids. For children and teens, BMI is age and sex-specific and is often called "BMI-for-age."
The BMI Formula
Metric System:
BMI = weight (kg) ÷ [height (m)]²
Imperial System:
BMI = [weight (lbs) ÷ height (inches)²] × 703
👶Why BMI is Different for Children
Children's bodies change significantly as they grow. Body fat changes with age, and boys and girls develop differently. That's why BMI for children must be compared to other children of the same age and sex.
📈Growth Charts & Percentiles
Doctors use CDC growth charts to plot a child's BMI and see where they fall compared to other children:
- •Below 5th percentile: Underweight
- •5th to 85th percentile: Healthy weight
- •85th to 95th percentile: Overweight
- •95th percentile and above: Obese
⚖️Body Changes with Age
Children naturally go through periods where BMI changes:
- •BMI decreases during preschool years
- •BMI increases again starting around age 6
- •Growth spurts affect BMI temporarily
- •Puberty causes major body composition changes
Important to Remember
A child's BMI percentile is more important than the BMI number itself. The percentile shows how a child's BMI compares with other children of the same age and sex.
✅What BMI Can and Cannot Tell You
✓What BMI CAN Do
- •Provide a useful screening tool for potential weight issues
- •Track changes in weight status over time
- •Help identify children who may benefit from health interventions
- •Start conversations about healthy habits
✗What BMI CANNOT Do
- •Measure body fat directly - it's just an estimate
- •Distinguish between fat, muscle, and bone mass
- •Account for athletic build or muscle development
- •Replace professional medical evaluation
💡Remember
BMI is just one tool. Your pediatrician will also consider your child's overall health, family history, diet, activity level, and other factors when assessing weight status.
⚠️When to Talk to Your Doctor
While you can calculate BMI at home, always consult your pediatrician for interpretation and guidance. Contact your doctor if:
🔴High BMI Concerns
- •Your child's BMI is above the 85th percentile
- •Rapid weight gain over a short period
- •Family history of obesity or related conditions
- •Concerns about diet or physical activity
🔵Low BMI Concerns
- •Your child's BMI is below the 5th percentile
- •Noticeable weight loss or failure to gain weight
- •Poor appetite or eating difficulties
- •Signs of malnutrition or growth delays
💪Promoting a Healthy Weight
Regardless of BMI, all children benefit from healthy eating and regular physical activity. Focus on building healthy habits as a family:
🥗Balanced Nutrition
- ✓Serve fruits and vegetables at every meal
- ✓Choose whole grains over refined grains
- ✓Include lean proteins
- ✓Limit sugary drinks and snacks
🏃Physical Activity
- ✓60+ minutes of activity daily
- ✓Make it fun with games and sports
- ✓Limit screen time to 2 hours/day
- ✓Be active as a family
😴Healthy Habits
- ✓Ensure adequate sleep (9-12 hours)
- ✓Eat meals together as a family
- ✓Avoid using food as reward/punishment
- ✓Be a healthy role model
Focus on Health, Not Weight
Avoid focusing on the number on the scale or making negative comments about weight. Instead, emphasize being strong, healthy, and feeling good. Positive approaches to health help children develop a healthy relationship with food and their bodies.
Related Topics
⚠️Important Medical Information
This BMI calculator and information are for educational purposes only and should not replace professional medical advice.
BMI interpretation for children requires professional medical evaluation using age and gender-specific growth charts. Only your pediatrician can accurately assess your child's BMI and determine appropriate interventions if needed.
Always consult with your child's doctor before making significant changes to diet or physical activity, especially if you have concerns about your child's weight or growth.