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When do babies sit up?

The CDC's milestone checklist lists “Sits without support” by 9 months, along with “Gets to a sitting position by herself.” By 6 months it lists “Leans on hands to support herself when sitting.” Most babies (75% or more) do these by those ages, and many sooner. If your baby isn't sitting alone by 9 months, ask your pediatrician.

Checked October 29, 2026.

What the CDC's checklists say

Milestones from the CDC's “Learn the Signs. Act Early.” checklists, word for word
ByThe CDC's milestoneMonth page
6 monthsLeans on hands to support herself when sittingYour baby at 6 months
9 monthsSits without supportYour baby at 9 months
9 monthsGets to a sitting position by herselfYour baby at 9 months

Each row is from the CDC's checklist for that age (6 months, 9 months), checked October 29, 2026.

What “by 9 months” means

Developmental milestones are things most children (75% or more) can do by a certain age. The CDC puts each milestone at the age by which at least 75% of children would be expected to do it, so that even one missing milestone leads to a conversation with the doctor instead of “wait and see”. So “by 9 months” isn't an average. Many children do it sooner, and the checklists don't list everything a child learns.

What it can look like

First sitting propped on their hands, then sitting alone with their hands free to play, then getting into a sit on their own.

What helps

  • Sit your baby between your legs or in a ring of cushions with a toy in front of them. Stay right there; babies tip over.
  • Put toys a little to the side so they practice turning and reaching while sitting.
  • Plenty of floor time. Rolling and pushing up build the strength sitting needs.

Talk to your pediatrician if…

Your baby isn't doing this by 9 months, the age on the CDC's list, has lost a skill they once had, or you're worried for any reason.

You know your child best. Don't wait. 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, share your concerns, and ask about developmental screening.

If you or the doctor are still concerned, the CDC says to ask for a referral to a specialist, and to call your state's early intervention program (find the number on the CDC's list). You do not need to wait for a doctor's referral or a medical diagnosis to make this call. If your child is younger than 3 years old, contact your local early intervention system.

More from the CDC: Concerned about your child's development? If your child seems unwell, call your pediatrician, or 911 in an emergency.

Sources