The WHO Motor Development Study put the normal window for hands-and-knees crawling between roughly month 5 and month 14 — and reported that about 1 in 23 healthy children never crawled on hands and knees at all. In more than 51,000 Wermom App logs, the curve looks almost identical — which is exactly why crawling is no longer on the CDC's milestone checklist.
For decades, crawling held a near-mythical place in the parenting imagination: the proof that a baby was "on track," the developmental beat that supposedly had to come before walking, the thing grandparents asked about first. The evidence never supported that weight. Crawling is one of the most variable, least predictive, and most frequently skipped motor milestones in the first year — and in 2022 it was quietly removed from the official U.S. developmental surveillance checklist3.
The WHO Motor Development Study, the largest and most rigorous prospective study of gross motor milestones in healthy children, followed 816 infants across Ghana, India, Norway, Oman, and the USA, assessed monthly through the first year by trained fieldworkers. It established "windows of achievement" — the 1st-to-99th percentile age band — for six milestones. For hands-and-knees crawling, that window ran from month 5.2 to month 13.5. And it found that 4.3% of these healthy children never demonstrated hands-and-knees crawling at all, going straight from sitting or belly-crawling to pulling up and walking1.
That single statistic is why crawling cannot be a screening milestone: you cannot flag the absence of a behavior that roughly 1 in 23 typically developing children never show. The question this analysis answers is the parent-facing one: across a large contemporary cohort, when does crawling actually happen, how wide is the spread, and how often is it skipped?
Across the full cohort, the median age at first parent-confirmed hands-and-knees crawling was month 8.4, with a 25-to-75 interquartile band running from month 7.3 to month 9.6. The 10th percentile was month 6.4; the 90th percentile was month 11.2. The shape and location of the Wermom curve track the WHO window closely, with the Wermom median sitting near the center of the WHO 5.2–13.5 month band1.
Two features of the curve matter for parents. First, the spread is genuinely wide — almost five months separate the 10th and 90th percentiles. A baby crawling at month 6 and a baby crawling at month 11 are both completely ordinary. Second, the curve has no clinically meaningful "late" threshold of its own, because crawling is not a checklist milestone. A baby who isn't crawling at 10 months is not, by that fact, behind. What matters at that age is the broader picture: are they sitting steadily, bearing weight on their legs, reaching and transferring objects, and finding some way to get to a toy across the room?
Of the 51,204 infants in the cohort, 2,867 (5.6%) logged independent walking with an explicit "never crawled on hands and knees" tag. This is slightly higher than the WHO study's 4.3% — plausibly because the Wermom definition strictly excluded belly-crawling and bottom-scooting, so an infant who only ever commando-crawled or scooted before walking would land in the "skipped hands-and-knees crawling" group1.
Within that group, the most common alternative locomotion patterns parents logged before walking were:
One reason crawling generates anxiety is that it overlaps in time with milestones parents consider more advanced. In the WHO study, the windows of achievement overlap substantially: sitting without support is the narrowest window (1st–99th percentile spanning month 3.8 to month 9.2), while standing with assistance and even walking with assistance windows begin before crawling's window closes1. In other words, a baby can be pulling to stand and cruising furniture before — or entirely without — ever crawling on hands and knees.
In the Wermom cohort, this sequence overlap was visible directly: among infants who did crawl, 22.4% logged "pulls to stand" before their first hands-and-knees crawl. The classic textbook order (sit, crawl, pull-to-stand, cruise, walk) is a central tendency, not a rule. The WHO study itself found that about 90% of children achieved five of the six milestones in a common sequence — but hands-and-knees crawling was the milestone most likely to fall out of that sequence or be skipped1.
In February 2022, the CDC — working with the AAP and the editor of Bright Futures — published the first major revision of its "Learn the Signs. Act Early." developmental milestone checklists in a peer-reviewed Pediatrics article3. Two changes are relevant here. First, the milestones were re-anchored to the age by which 75% of children demonstrate a skill (rather than the prior 50% "average age" framing), so that a child who hasn't met a listed milestone is more clearly an outlier worth a conversation7. Second, crawling was removed entirely from the checklist.
The stated reasons map exactly onto what large datasets show: a lack of robust normative data, inconsistent definitions of "crawling," wide variability in onset, and the well-documented fact that many typically developing children never crawl on hands and knees3. The CDC's 9-month checklist now lists milestones like getting to a sitting position without help and moving things from one hand to the other — observable, well-normed, and predictive — rather than crawling4.
Because crawling is off the checklist, the surveillance question shifts to the milestones around it. Per the CDC/AAP milestone framework and Bright Futures health-supervision guidance, a developmental conversation with the pediatrician is reasonable when a healthy term infant46:
Any of these merits evaluation regardless of whether crawling has happened. Equally, an 11-month-old who scoots, cruises, babbles, and reaches symmetrically but has never crawled on hands and knees needs reassurance, not a referral.
This is descriptive epidemiology from a self-selected, app-using cohort, and three limitations bear emphasis. First, app-using parents may differ from the general population in ways (income, education, vigilance of logging) that could shift detected timing earlier rather than later. Second, "first hands-and-knees crawl" depends on parental observation and the app's definitional prompts; the strict exclusion of belly-crawling and scooting makes the Wermom "skip" rate an upper-ish bound relative to looser definitions. Third, the cohort excludes infants with documented neuromuscular or genetic diagnoses or prolonged NICU stays, so the curve describes healthy term infants and should not be used to interpret motor timing in medically complex children, where specialist guidance applies.
Future Wermom analyses planned for 2026–2027 will examine: (a) the relationship between logged daily tummy-time minutes and crawling onset, (b) whether crawl-skippers reach independent walking earlier, later, or at the same age as crawlers, and (c) the sequence relationship between sitting, crawling, and pulling-to-stand within same-infant logs.
Hands-and-knees crawling in a healthy term infant has a population median around month 8 and a normal window stretching from roughly month 6 to month 12, mirroring the WHO Motor Development Study's window of achievement. About 1 in 18 infants in this cohort skipped hands-and-knees crawling entirely and went straight to walking — which is precisely why crawling was removed from the CDC/AAP developmental surveillance checklist in 2022. Crawling is interesting, but it is not a test. The milestones worth watching are sitting independently, bearing weight on the legs, moving across a room by any self-generated method by 12 months, and symmetrical use of both sides of the body. A baby who is doing those things and hasn't crawled is doing fine.
The Wermom App shows your child's milestone log against the same WHO and CDC reference windows used in this research — so you can see where you are in the distribution, not just whether you've ticked a box.
Open the Wermom AppThis is general health information, not medical advice, and not a substitute for professional care. Educational content evidence-checked against AAP & NHS guidance.
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