Baby Developmental Milestones Month-by-Month (0–24 Months)

Evidence-based developmental milestones, the wide normal-variation range, and the specific thresholds that warrant an Early Intervention referral this week — not next year.

By Wermom Editorial · Reviewed against AAP, CDC Developmental Milestones (2022 update), Early Intervention guidelines · Last updated 2026-05-27

The milestone framework — why "average" is a range

The CDC updated its developmental milestone checklists in 2022 to reflect when 75% of children achieve each milestone, rather than the older "average age" framing. This shift matters because the older framing made many parents anxious about children doing perfectly normal things at the slow end of normal.

Three concepts to internalize:

1. Wide normal range. A milestone might be achieved by 25% of babies at age X and 95% of babies by age Y. The range between X and Y is normal variation, not a problem.
2. Individual variation by domain. A baby may be early on motor milestones and slow on language, or vice versa. This is normal. Concern is warranted when MULTIPLE domains are simultaneously delayed.
3. Trajectory matters more than absolute timing. A baby who is consistently 1-2 months "late" on each milestone but progressing on the same curve is different from a baby who hit milestones on time, then stopped progressing.

Months 0–3: organizing the world

The first 3 months are about regulation. Sleep-wake cycles begin to organize. The baby learns to extract pattern from sensory chaos. Most "milestones" in this window are physiological rather than behavioral.

Months 3–6: discovery

Months 6–9: mobility begins

Months 9–12: explorers

Months 12–18: walking and first words

Months 18–24: language explosion + independence

Red flag thresholds by age — call Early Intervention

These are not "average ages" — they are thresholds where evaluation is warranted regardless of "wait and see" advice. The earlier intervention starts, the more effective it typically is.

By 6 months — CALL if:

• Doesn't try to get things within reach
• Shows no affection for caregivers
• Doesn't respond to sounds around them
• Has difficulty getting things to mouth
• Doesn't make vowel sounds ("ah," "eh," "oh")
• Doesn't roll over in either direction
• Doesn't laugh or make squealing sounds

By 9 months — CALL if:

• Doesn't bear weight on legs with support
• Doesn't sit with help
• Doesn't babble ("mama," "baba," "dada")
• Doesn't play any games involving back-and-forth play
• Doesn't respond to own name
• Doesn't seem to recognize familiar people
• Doesn't look where you point
• Doesn't transfer toys from one hand to the other

By 12 months — CALL if:

• Doesn't crawl
• Can't stand when supported
• Doesn't search for objects you hide
• Doesn't say single words like "mama" or "dada"
• Doesn't learn gestures like waving or shaking head
• Doesn't point to things
• Loses skills they once had

By 18 months — CALL if:

• Can't walk
• Doesn't know what familiar things are for (cup for drinking, etc.)
• Doesn't copy others
• Doesn't gain new words
• Doesn't have at least 6 words
• Doesn't notice or mind when a caregiver leaves or returns
• Loses skills they once had

By 24 months — CALL if:

• Doesn't use 2-word phrases (e.g., "drink milk")
• Doesn't know what to do with common things, like a brush, phone, fork, spoon
• Doesn't copy actions and words
• Doesn't follow simple instructions
• Doesn't walk steadily
• Loses skills they once had

What Early Intervention actually does (and why to call early)

Early Intervention (EI) is a federally-mandated, state-administered program providing free developmental services to children under 3 who have a developmental delay or are at risk. Services can include: developmental therapy, speech therapy, occupational therapy, physical therapy, behavioral therapy, family training and support.

To access EI, you don't need a referral from a pediatrician (though pediatricians often initiate). Parents can call their state's EI program directly. The first step is a comprehensive evaluation by a multi-disciplinary team. If your child qualifies, an Individualized Family Service Plan (IFSP) is created with specific goals and services.

The qualifying threshold is typically 25-33% delay in one or more domains, OR a diagnosed condition with high probability of developmental delay (Down syndrome, cerebral palsy, etc.).

Even if your child doesn't qualify for EI: the evaluation itself often catches subtle issues, and the recommendations (even informal) can guide your support at home. The downside of evaluation is essentially zero. The downside of waiting and missing the early-intervention window is significant.

State EI program contact: search "Early Intervention [your state]" or call CDC's Act Early at 1-800-CDC-INFO.

Regression vs slow progress — knowing the difference

Children sometimes appear to "lose" skills temporarily during illness, after a major life change (new baby, move, daycare transition), or during a developmental leap (energy goes to one skill, others recede). This typically resolves within 2-4 weeks.

True regression — losing skills and not regaining them — is different and warrants urgent evaluation. Examples:

• A child who had 15 words at 18 months but only 5 at 22 months — regression
• A child who walked at 13 months but stopped walking at 16 months — regression
• A child who made eye contact regularly but no longer makes eye contact — regression
• A child who recognized faces but no longer seems to — regression

True regression can be a sign of autism spectrum disorder (about 25-40% of children with autism show some form of regression, typically between 12-24 months), genetic conditions, neurological issues, or in rare cases, infections affecting the brain. None of these are diagnoses parents should be making at home — they're indications to seek immediate pediatric assessment and developmental evaluation.

Final thought

Developmental milestones are a guide, not a test. Most variation between babies is normal — being 1-2 months behind on a single milestone while progressing on others is rarely meaningful. The trajectory matters more than any single date.

But specific red-flag thresholds exist for a reason. Early intervention works dramatically better at 14 months than at 30 months. The cost of unnecessary evaluation is essentially zero; the cost of missing the early-intervention window can affect a child for years. When in doubt, call. The evaluation costs nothing and tells you what you need to know.

And — important — your baby is more than a checklist. The smile that breaks your heart, the way they reach for you specifically, the singular humor of their personality emerging — none of that shows up in milestone tracking. Track for early-intervention purposes. Live for the moments.