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When do babies understand no?

The CDC's milestone checklist lists “Understands “no” (pauses briefly or stops when you say it)” by 1 year. That means most babies (75% or more) pause or stop when you say no by their first birthday. The CDC's words describe a pause or a stop, not always listening. If you're worried, talk with 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
1 yearUnderstands “no” (pauses briefly or stops when you say it)Your baby at 12 months

Each row is from the CDC's checklist for that age (1 year), checked October 29, 2026.

What “by 1 year” 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 1 year” isn't an average. Many children do it sooner, and the checklists don't list everything a child learns.

What it can look like

A pause, a look back at you, or stopping for a moment when you say no.

What helps

  • Say "No" calmly and clearly, then show what they can do instead.
  • Save "no" for things that matter, so it stands out.
  • Make your home safer to explore, so you need to say it less.

Talk to your pediatrician if…

Your baby isn't doing this by 1 year, 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