📖 Baby Milestone Guide Reference
A general reference of commonly cited developmental milestones by age. Every baby develops at their own pace — this is informational only, not medical advice. Talk to your pediatrician with any concerns.
What a milestone list actually is
Lists like this one summarise what most children of an age are already doing. They come out of population data, not from any theory of what a child should do by a date. The best-known set, the CDC and American Academy of Pediatrics "Learn the Signs. Act Early." checklists, was rewritten in 2022 around the 75th percentile - skills about three quarters of children have at that age - because the older 50th-percentile lists left parents unsure what missing one meant.
The CDC set is pinned to the ages of routine check-ups: 2, 4, 6, 9, 12, 15, 18, 24 and 30 months. The bands in the filter above are broader, so read an entry as "somewhere in this stretch", never as a date.
How wide the normal range is
The WHO motor development study followed healthy children in six countries and published the age windows in which 99 percent of them reached each motor skill:
| Skill | Window (months) |
|---|---|
| Sitting without support | 3.8 - 9.2 |
| Hands-and-knees crawling | 5.2 - 13.5 |
| Standing alone | 6.9 - 16.9 |
| Walking alone | 8.2 - 17.6 |
A window that wide is why one late skill tells you very little on its own. What health services do ask you to report is different in kind: a skill the child once had and has lost.
Frequently asked questions
At what age do babies walk?
Most walk alone between 12 and 15 months, but the WHO study puts the normal window at 8.2 to 17.6 months. Walking at nine months and at sixteen are both inside it.
Should I worry if my baby never crawled?
Crawling on hands and knees is not on the current CDC checklists at all. Plenty of babies shuffle, roll or bottom-scoot and then walk.
What does the 75th percentile mean on a milestone chart?
That about 75 percent of children can do it by that age. It is a marker for starting a conversation, not a deadline - roughly a quarter of typical children are still to reach it.