Baby Growth Percentile Examples: 5 Worked Cases by Age

July 15, 2026

Seeing the LMS formula applied to real ages and measurements makes it click faster than the formula alone. Each example below uses the official published L, M, and S values and the same math the baby percentile calculator runs. For the formula itself, see the calculator’s methodology section; for term definitions, see the growth percentile glossary.

Example 1 — 1-Month-Old Boy, 4.6 kg (Weight-for-Age)

WHO LMS values for boys at 1 month: L = 1.308, M = 4.441 kg, S = 0.141.

Z = ((4.6 / 4.441)^1.308 − 1) / (1.308 × 0.141) = 0.25
Percentile = Φ(0.25) × 100 ≈ 60th percentile

A touch above the median for 1-month-old boys — well within the typical range.

Example 2 — 9-Month-Old Boy, 8.0 kg (Weight-for-Age)

WHO LMS values for boys at 9 months: L = -0.147, M = 9.279 kg, S = 0.113.

Z = ((8.0 / 9.279)^-0.147 − 1) / (-0.147 × 0.113) = -1.33
Percentile = Φ(-1.33) × 100 ≈ 9th percentile

Still inside the normal 3rd-97th percentile band, but on the lighter end. A single reading like this is common and often reflects a naturally smaller-framed baby — see common growth percentile mistakes for why the trend across visits matters more than one number like this in isolation.

Example 3 — 12-Month-Old Girl, 73.0 cm (Height/Length-for-Age)

WHO LMS values for girls at 12 months: L = 1.524, M = 73.790 cm, S = 0.039.

Z = ((73.0 / 73.790)^1.524 − 1) / (1.524 × 0.039) = -0.27
Percentile = Φ(-0.27) × 100 ≈ 39th percentile

Just below the median for 12-month-old girls’ length — a completely typical result.

Example 4 — 5-Year-Old Girl, 17.0 kg (Weight-for-Age)

At age 5, this measurement uses the CDC 2000 chart instead of the WHO chart. CDC LMS values for girls at 5 years: L = -1.284, M = 17.930 kg, S = 0.141.

Z = ((17.0 / 17.930)^-1.284 − 1) / (-1.284 × 0.141) = -0.39
Percentile = Φ(-0.39) × 100 ≈ 35th percentile

Example 5 — 15-Year-Old Boy, 170 cm (Height-for-Age)

CDC LMS values for boys at 15 years: L = 2.196, M = 169.940 cm, S = 0.046.

Z = ((170 / 169.940)^2.196 − 1) / (2.196 × 0.046) = 0.01
Percentile = Φ(0.01) × 100 ≈ 50th percentile

Essentially exact median height for a 15-year-old boy — as close to the 50th percentile as a real-world measurement gets.

What These Five Examples Show

Notice that a Z-score near 0 always lands close to the 50th percentile regardless of age, metric, or which chart (WHO or CDC) applies — the LMS method is built so the same Z-score means the same relative position at any age. Also notice Example 3 and Example 4 use L values with opposite signs (positive for the 12-month length, negative for the 5-year weight); the formula automatically handles both directions correctly, which is why hand-calculating this by eye off a printed chart is much more error-prone than using the exact LMS math.

Try your own child’s exact numbers in the baby percentile calculator — enter age (use corrected age if premature, see the premature and NICU parents’ guide), sex, and measurement to get the precise percentile and Z-score instantly, without doing this arithmetic by hand.