What the CDC checklists say
- By 6 months"Leans on hands to support himself when sitting"
- By 9 months"Sits without support"
- By 9 months"Gets to a sitting position by herself"
CDC milestones show what most children (75% or more) can do by each age, so many children do these things sooner.
The normal range is wide
The WHO Motor Development Study followed healthy children in five countries and recorded when each first reached six movement milestones. The bars show the ages by which 1% and 99% of them got there; sitting without support is highlighted.
The CDC says you know your child best. If your child is not meeting one or more milestones, has lost skills he or she once had, or you have other concerns, act early: talk with your child's doctor and ask about a developmental screening.
Related milestones
Frequently asked questions
When do babies sit up?
The CDC lists sitting without support by 9 months. In the WHO study, healthy babies first sat alone anywhere from 3.8 to 9.2 months.
When should I talk to a doctor?
The CDC says to act early if your baby is not meeting one or more milestones, has lost skills they once had, or you have other concerns. Talk with your child's doctor; you know your baby best.
Sources: CDC, "Learn the Signs. Act Early." milestone checklists; WHO Motor Development Study, Acta Paediatrica 95 (2006): 86-95. Checked October 17, 2026. Not medical advice. Our sources.