Is the 90th percentile good or bad?

It is an attainment age, not a height. The 90th percentile means nine children in ten were already doing this by that age, so it is on the late side. That is a position, not a verdict — what matters is whether it falls outside the window.

My child was earlier than the window start. Is that advanced?

This page will not say. WHO’s table begins at the 1st percentile and nothing is published before it, so all that can honestly be reported is that the age fell earlier than the window starts.

What should I do if it is past the end of the window?

WHO states in this standard that a child who has not reached a milestone by the end of its window warrants developmental review. Take the milestone, the child’s current age and what you have observed to a paediatrician.

Why only six milestones?

Because WHO published windows for six. The rest have no table to check against, and this site does not list milestones it cannot source.

Calculators

Motor milestone window

The age a child first did something, placed against a published distribution. WHO reports attainment age for six gross-motor milestones from the 1st to the 99th percentile, and this page reads that table.

WHO’s attainment window runs from 3.8 to 9.2 months (1st to 99th percentile).

This places the timing against a published distribution; it is not a diagnosis. WHO publishes windows for these six movements and no others, so nothing is said about the rest.

How to read this number

Milestone checklists ask whether a child does something. What parents want to know is whether it is late, and that takes different data: a checklist says what children this age are expected to do, while WHO’s 2006 motor standards report when the same movement is attained across a population — which is what makes “sitting at seven and a half months” answerable.

The percentile runs the opposite way from height. A 90th-percentile height is tall; a 90th-percentile attainment age is late — it means nine children in ten were already doing it by then. Higher is later, not better.

The window ends at the 1st and 99th percentiles, and so does the table. A child earlier than the start or later than the end is reported as outside the window rather than given an extrapolated figure nobody measured. WHO states it plainly: a child who has not reached a milestone by the end of its window warrants developmental review.

Six milestones, and only six. WHO publishes no window for rolling over, running, jumping or climbing stairs, so this page says nothing about them — where there is no table, there is no answer here.

The standard behind it

This calculator uses WHO Child Growth Standards (2006) · WHO Growth Reference (2007)’s LMS parameters. Ages 0–5 use the 2006 Child Growth Standards and 5–19 the 2007 growth reference; the two join at five.

The source tables are taken straight from who.int, data version 2026-09-02. Ages beyond what a standard covers are never extrapolated — the page says there is nothing there.

Common questions

Is the 90th percentile good or bad?: It is an attainment age, not a height. The 90th percentile means nine children in ten were already doing this by that age, so it is on the late side. That is a position, not a verdict — what matters is whether it falls outside the window.
My child was earlier than the window start. Is that advanced?: This page will not say. WHO’s table begins at the 1st percentile and nothing is published before it, so all that can honestly be reported is that the age fell earlier than the window starts.
What should I do if it is past the end of the window?: WHO states in this standard that a child who has not reached a milestone by the end of its window warrants developmental review. Take the milestone, the child’s current age and what you have observed to a paediatrician.
Why only six milestones?: Because WHO published windows for six. The rest have no table to check against, and this site does not list milestones it cannot source.