Bmi For Age Percentage Calculator

BMI for Age Percentage Formula:

\[ Z = \begin{cases} \frac{(BMI / M)^L - 1}{L \times S} & \text{if } L \neq 0 \\ \frac{\ln(BMI / M)}{S} & \text{if } L = 0 \end{cases} \] \[ \text{Percentile} = 100 \times \Phi(Z) \]

BMI Percentile:

Unit Converter ▲

Unit Converter ▼

From:	To:

1. What is BMI for Age Percentage?

The BMI-for-age percentage is a measure that compares a child's BMI to children of the same age and gender. It uses the LMS method (Lambda-Mu-Sigma) to calculate growth percentiles from standardized growth charts.

2. How Does the Calculator Work?

The calculator uses the LMS method formula:

\[ Z = \begin{cases} \frac{(BMI / M)^L - 1}{L \times S} & \text{if } L \neq 0 \\ \frac{\ln(BMI / M)}{S} & \text{if } L = 0 \end{cases} \] \[ \text{Percentile} = 100 \times \Phi(Z) \]

Where:

\( BMI \) — Body Mass Index (kg/m²)
\( M \) — Median BMI for age and gender
\( L \) — Box-Cox power (skewness)
\( S \) — Coefficient of variation
\( \Phi \) — Standard normal cumulative distribution

Explanation: The LMS method accounts for the non-normal distribution of BMI values in children and provides age- and gender-specific growth references.

3. Importance of BMI Percentile

Details: BMI percentile is the preferred measure for assessing weight status in children and adolescents. It helps identify underweight, healthy weight, overweight, and obesity categories.

4. Using the Calculator

Tips: Enter BMI in kg/m², age in years (2-20), and select gender. The calculator will determine the child's BMI percentile relative to peers of the same age and gender.

5. Frequently Asked Questions (FAQ)

Q1: What do the percentile results mean?
A: Below 5th = underweight; 5th-85th = healthy weight; 85th-95th = overweight; Above 95th = obese.

Q2: Why use percentiles instead of BMI categories?
A: Children's body composition changes with age, so percentiles account for normal growth patterns.

Q3: Where do the LMS values come from?
A: From CDC or WHO growth charts that provide age- and gender-specific L, M, and S values.

Q4: How accurate is this calculator?
A: For clinical use, consult official growth charts. This demonstrates the calculation method.

Q5: Can this be used for adults?
A: No, BMI percentiles are only meaningful for children and adolescents (2-20 years).