Infant BMI Calculator With Percentile

LMS Method Formula:

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

BMI:

kg/m²

Median BMI (M):

kg/m²

Box-Cox Power (L):

Coefficient of Variation (S):

Z-Score:

Percentile:

Unit Converter ▲

Unit Converter ▼

From:	To:

1. What is the LMS Method?

The LMS method is a statistical technique used to calculate growth percentiles in children. It uses three parameters: L (Box-Cox power), M (median), and S (coefficient of variation) to account for the skewness of growth data.

2. How Does the Calculator Work?

The calculator uses the LMS 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 sex (kg/m²)
\( L \) — Box-Cox power (unitless)
\( S \) — Coefficient of variation (unitless)
\( \Phi \) — Standard normal cumulative distribution

Explanation: The LMS method transforms skewed growth data to normality, allowing accurate percentile calculation.

3. Importance of BMI Percentile

Details: BMI percentile is crucial for assessing infant growth patterns and identifying potential undernutrition or overweight. It accounts for age and sex differences in body composition.

4. Using the Calculator

Tips: Enter the infant's BMI, along with the appropriate LMS values (M, L, S) from growth charts. All values must be positive.

5. Frequently Asked Questions (FAQ)

Q1: Where do I find LMS parameters?
A: LMS parameters are available in published growth charts (WHO, CDC) specific to age, sex, and population.

Q2: What is a normal BMI percentile?
A: Typically 5th to 85th percentile is considered healthy, but consult pediatric growth standards.

Q3: Why use LMS instead of simple percentiles?
A: LMS accounts for the non-normal distribution of growth data, providing more accurate extremes.

Q4: Can this be used for older children?
A: Yes, but ensure you use age- and sex-specific LMS parameters.

Q5: How precise is this calculation?
A: Very precise when using correct LMS values. Clinical judgment should accompany results.