How it is calculated
The calculator uses the WHO Child Growth Standards (2006) with the LMS method:
Z = ((X ÷ M)^L − 1) ÷ (L × S)where X is your child’s measurement and L, M, S come from the table for their age and sex. Z is converted to a percentile: 50 is average; 25 means 25% of healthy children measure less.
| Percentile | General meaning |
|---|---|
| Below 3 | Low — worth assessing |
| 3 – 97 | Typical range |
| Above 97 | High — worth assessing |
Worked example
A 6-month-old boy weighing 7.9 kg: the median at this age is 7.93 kg, so he sits around the 48th percentile — right in the middle.
Frequently asked questions
Is a low percentile worrying?
Not necessarily — what matters is following a consistent curve. Crossing two major lines downward warrants a doctor’s review.
Does it work for premature babies?
Use the corrected age until age 2: subtract the weeks of prematurity.
Why WHO standards?
They are based on healthy breastfed children from several countries and are used by most countries.