How should a baby develop month by month, and what are the developmental milestones?
Applies to age: 0–12 months
In short
A child's development does not follow a strict pattern. In the WHO study, healthy children (1st–99th percentile) sat without support at 3.8–9.2 months and walked alone at 8.2–17.6 months. A doctor assesses the pace of psychomotor development at the well-child checkups at 9 and 12 months.
What is normal
Some claims: international norm
- In the WHO study, the window for achieving "sitting without support" in healthy children is 3.8–9.2 months; the limits are the 1st and 99th percentile.
Source: WHO · international norm – show the original wording (EN)
Summarized and translated by the editors, not an official translation. Verbatim quote from the source, in its original wording:
The estimated 1st and 99th percentiles in months are: 3.8, 9.2 (sitting without support), 4.8, 11.4 (standing with assistance), 5.2, 13.5 (hands-and-knees crawling), 5.9, 13.7 (walking with assistance), 6.9, 16.9 (standing alone) and 8.2, 17.6 (walking alone).
WHO · open the source · accessed: 2026-10-09 · license [1]
- In the WHO study, the window for achieving "standing with support" in healthy children is 4.8–11.4 months; the limits are the 1st and 99th percentile.
Source: WHO · international norm – show the original wording (EN)
Summarized and translated by the editors, not an official translation. Verbatim quote from the source, in its original wording:
The estimated 1st and 99th percentiles in months are: 3.8, 9.2 (sitting without support), 4.8, 11.4 (standing with assistance), 5.2, 13.5 (hands-and-knees crawling), 5.9, 13.7 (walking with assistance), 6.9, 16.9 (standing alone) and 8.2, 17.6 (walking alone).
WHO · open the source · accessed: 2026-10-09 · license [1]
- In the WHO study, the window for achieving hands-and-knees crawling in healthy children is 5.2–13.5 months; the limits are the 1st and 99th percentile.
Source: WHO · international norm – show the original wording (EN)
Summarized and translated by the editors, not an official translation. Verbatim quote from the source, in its original wording:
The estimated 1st and 99th percentiles in months are: 3.8, 9.2 (sitting without support), 4.8, 11.4 (standing with assistance), 5.2, 13.5 (hands-and-knees crawling), 5.9, 13.7 (walking with assistance), 6.9, 16.9 (standing alone) and 8.2, 17.6 (walking alone).
WHO · open the source · accessed: 2026-10-09 · license [1]
- In the WHO study, the window for achieving "walking with support" in healthy children is 5.9–13.7 months; the limits are the 1st and 99th percentile.
Source: WHO · international norm – show the original wording (EN)
Summarized and translated by the editors, not an official translation. Verbatim quote from the source, in its original wording:
The estimated 1st and 99th percentiles in months are: 3.8, 9.2 (sitting without support), 4.8, 11.4 (standing with assistance), 5.2, 13.5 (hands-and-knees crawling), 5.9, 13.7 (walking with assistance), 6.9, 16.9 (standing alone) and 8.2, 17.6 (walking alone).
WHO · open the source · accessed: 2026-10-09 · license [1]
- In the WHO study, the window for achieving "standing alone" in healthy children is 6.9–16.9 months; the limits are the 1st and 99th percentile.
Source: WHO · international norm – show the original wording (EN)
Summarized and translated by the editors, not an official translation. Verbatim quote from the source, in its original wording:
The estimated 1st and 99th percentiles in months are: 3.8, 9.2 (sitting without support), 4.8, 11.4 (standing with assistance), 5.2, 13.5 (hands-and-knees crawling), 5.9, 13.7 (walking with assistance), 6.9, 16.9 (standing alone) and 8.2, 17.6 (walking alone).
WHO · open the source · accessed: 2026-10-09 · license [1]
- In the WHO study, the window for achieving "walking alone" in healthy children is 8.2–17.6 months; the limits are the 1st and 99th percentile.
Source: WHO · international norm – show the original wording (EN)
Summarized and translated by the editors, not an official translation. Verbatim quote from the source, in its original wording:
The estimated 1st and 99th percentiles in months are: 3.8, 9.2 (sitting without support), 4.8, 11.4 (standing with assistance), 5.2, 13.5 (hands-and-knees crawling), 5.9, 13.7 (walking with assistance), 6.9, 16.9 (standing alone) and 8.2, 17.6 (walking alone).
WHO · open the source · accessed: 2026-10-09 · license [1]
- The WHO motor development windows describe the normal variation in the age at which healthy children reach milestones.
Source: WHO · international norm – show the original wording (EN)
Summarized and translated by the editors, not an official translation. Verbatim quote from the source, in its original wording:
The windows represent normal variation in ages of milestone achievement among healthy children.
WHO · open the source · accessed: 2026-10-09 · license [1]
- In the WHO study, about 90% of children reached five of the six milestones in the same order, and 4.3% of children were not observed to crawl on hands and knees.
Source: WHO · international norm – show the original wording (EN)
Summarized and translated by the editors, not an official translation. Verbatim quote from the source, in its original wording:
About 90% of children achieved five of the milestones following a common sequence, and 4.3% did not exhibit hands-and-knees crawling.
WHO · open the source · accessed: 2026-10-09 · license [1]
- Every child is different, and a child's development does not follow a strict pattern.
Source: Portal Pacjenta – show the quote
Verbatim quote from the source:
Polish original
Każde dziecko jest inne i jego rozwój nie przebiega ściśle według wzorca.
Portal Pacjenta · open the source · accessed: 2026-10-09 · license [2]
- Children differ in the pace of their speech and language development.
Source: NIDCD · international norm – show the original wording (EN)
Summarized and translated by the editors, not an official translation. Verbatim quote from the source, in its original wording:
Children vary in their development of speech and language skills.
NIDCD · open the source · accessed: 2026-10-09 · license [3]
- Newborns begin to recognize important sounds in their surroundings, for example the voice of their mother or main caregiver.
Source: NIDCD · international norm – show the original wording (EN)
Summarized and translated by the editors, not an official translation. Verbatim quote from the source, in its original wording:
Newborns also begin to recognize important sounds in their environment, such as the voice of their mother or primary caretaker.
NIDCD · open the source · accessed: 2026-10-09 · license [3]
- At 6 months of age, most babies recognize the basic sounds of their native language.
Source: NIDCD · international norm – show the original wording (EN)
Summarized and translated by the editors, not an official translation. Verbatim quote from the source, in its original wording:
By 6 months of age, most babies recognize the basic sounds of their native language.
NIDCD · open the source · accessed: 2026-10-09 · license [3]
- The hearing and communication development checklist for the age of 7 months–1 year lists one or two words (for example "Hi", "dog", "Dada", "Mama") by the first birthday.
Source: NIDCD · international norm – show the original wording (EN)
Summarized and translated by the editors, not an official translation. Verbatim quote from the source, in its original wording:
Has one or two words (“Hi,” “dog,” “Dada,” or “Mama”) by first birthday
NIDCD · open the source · accessed: 2026-10-09 · license [3]
When to worry
All claims: international norm
- The WHO developmental windows are meant, among other things, to signal the need for appropriate screening when individual children appear to be late in reaching milestones.
Source: WHO – show the original wording (EN)
Summarized and translated by the editors, not an official translation. Verbatim quote from the source, in its original wording:
They are recommended for descriptive comparisons among populations, to signal the need for appropriate screening when individual children appear to be late in achieving the milestones, and to raise awareness about the importance of overall development in child health.
WHO · open the source · accessed: 2026-10-09 · license [1]
See a doctor
- Polish care path: the Ministry of Health (MZ) regulation on guaranteed services in primary care (POZ) (consolidated text, Journal of Laws (Dz.U.) 2023, item 1427, Annex 1, Part III, item 1) provides, in the 1st–4th week of life, for a newborn (patronage) consultation with a POZ doctor that includes an examination covering physical development. This is the timing of the consultation, not an age range for skills.
Source: Akty prawne w Dzienniku Ustaw – show the quote
Verbatim quote from the source:
Polish original
Porada patronażowa lekarza podstawowej opieki zdrowotnej, obejmująca badanie podmiotowe i przedmiotowe, z uwzględnieniem rozwoju fizycznego
Akty prawne w Dzienniku Ustaw · open the source · accessed: 2026-10-09 · license [4]
- Polish care path: the MZ regulation on guaranteed services in POZ (consolidated text, Dz.U. 2023, item 1427, Annex 1, Part III, item 2) provides, for the 2nd–6th month of life (at times matching the protective vaccinations), for a medical examination covering physical development, past illnesses and the prevention of rickets. This is the timing of the well-child checkup, not an age range for skills.
Source: Akty prawne w Dzienniku Ustaw – show the quote
Verbatim quote from the source:
Polish original
Badanie lekarskie podmiotowe i przedmiotowe, z uwzględnieniem rozwoju fizycznego (pomiary: masy i długości ciała, obwodu głowy i klatki piersiowej), przebytych schorzeń oraz zapobiegania krzywicy.
Akty prawne w Dzienniku Ustaw · open the source · accessed: 2026-10-09 · license [4]
- Polish care path: the MZ regulation on guaranteed services in POZ (consolidated text, Dz.U. 2023, item 1427, Annex 1, Part III, items 3 and 4) provides, for the 9th and 12th month of life, for a medical examination covering the pace of psychomotor development. These are the timings of the well-child checkups and an indication of who assesses development, not age ranges for skills.
Source: Akty prawne w Dzienniku Ustaw – show the quote
Verbatim quote from the source:
Polish original
Badanie lekarskie podmiotowe i przedmiotowe, z uwzględnieniem tempa rozwoju fizycznego (pomiary: masy i długości ciała, obwodu głowy i klatki piersiowej) i psychomotorycznego.
Akty prawne w Dzienniku Ustaw · open the source · accessed: 2026-10-09 · license [4]
- The Patient Portal (Portal Pacjenta) of the MZ and the National Health Fund (NFZ) describes the child's well-child checkup as an examination that makes it possible to check whether the child is developing properly and to detect developmental defects and illnesses early.
Source: Portal Pacjenta – show the quote
Verbatim quote from the source:
Polish original
Pozwala sprawdzić, czy Twoje dziecko rozwija się prawidłowo oraz wcześnie wykryć wady rozwojowe i choroby
Portal Pacjenta · open the source · accessed: 2026-10-09 · license [2]
- If something about your child's development worries you, it is worth consulting a specialist and making use of the advice of a midwife, a nurse or a pediatrician.
Source: Portal Pacjenta – show the quote
Verbatim quote from the source:
Polish original
Warto jednak skonsultować ze specjalistą to, co Cię zaniepokoiło i korzystać z rad położnej, pielęgniarki czy pediatry.
Portal Pacjenta · open the source · accessed: 2026-10-09 · license [2]
international norm “International norm” next to a section heading means its claims come from a non-Polish source, because no Polish source in our registry covers this topic. When this applies to only some of the claims, the foreign ones carry the same label next to their source.
Sources
- WHO (who.int)License: CC BY-NC-SA 3.0 IGO. Source: WHO (who.int). Content summarized and translated by the editors; changed relative to the original. WHO does not endorse this site or its content.
- Portal Pacjenta (pacjent.gov.pl)
- https://pacjent.gov.pl/zapobiegaj/jak-dbac-o-zdrowy-rozwoj-psychiczny-dziecka
- https://pacjent.gov.pl/zapobiegaj/zaprowadz-dziecko-na-bilans-zdrowia
License: CC BY 3.0 PL. Source: Portal Pacjenta (pacjent.gov.pl). Content summarized and translated by the editors; changed relative to the original. - NIDCD – Speech and Language Developmental Milestones (USA)License: Domena publiczna (USA). Source: NIDCD – Speech and Language Developmental Milestones (USA).
- Akty prawne w Dzienniku Ustaw (ELI: eli.gov.pl, api.sejm.gov.pl)License: Akt normatywny, art. 4 pkt 1 ustawy o prawie autorskim (nie podlega ochronie). Source: Akty prawne w Dzienniku Ustaw (ELI: eli.gov.pl, api.sejm.gov.pl).