Understanding Baby Development: A Week-by-Week Guide for the First Year

Reviewed for general-information accuracy against CDC and AAP developmental-milestone guidance. This guide is for general information and is not medical advice — every baby develops at their own pace; talk to your pediatrician about your baby’s individual development.

Baby development in the first year: the quick answer

Across the first year, most babies move from reflexive newborns to little explorers who sit, babble, and often take a first step — usually progressing through social, language, cognitive, and physical (motor) milestones. But timing varies widely and that is normal: the CDC defines a milestone as something most children (75% or more) can do by a certain age, not a pass-or-fail test. Use the stages below as a friendly map, celebrate progress in any order, and talk to your pediatrician if your baby misses several milestones for their age or loses a skill they once had.

Below you’ll find a stage-by-stage guide for the whole first year, a quick-reference milestone table, simple ways to support each stage, and answers to the questions parents ask most.

How to read milestones (so you don’t worry needlessly)

Milestones are a guide, not a deadline. The CDC “Learn the Signs. Act Early.” checklists (updated with the AAP in 2022) list what most babies can do by a given age, and the World Health Organization documents wide normal “windows” for big motor skills — independent walking, for example, can normally appear anywhere from about 8 to 18 months. Premature babies are usually tracked by their corrected age. The goal isn’t to hit each item on an exact week; it’s steady forward progress, with your pediatrician as your partner at every well-child visit.

First-year milestones at a glance

This quick-reference table summarizes typical milestones by stage. Ranges overlap on purpose — your baby may reach some earlier and some later.

Stage	Social & emotional	Language	Cognitive	Movement / physical
Newborn (0–1 mo)	Calms to your voice; looks at your face	Cries; begins cooing “ahh” sounds	Focuses ~8–14 in; tracks briefly	Turns head; reflexive grasp; lifts head a little on tummy
~2 months	First real smile; happy to see you	Makes sounds other than crying; reacts to loud sounds	Watches you move; looks at a toy	Holds head up on tummy; moves both arms & legs
~4 months	Smiles to get attention; chuckles	Coos; turns toward your voice	Looks at hands; opens mouth when hungry	Holds head steady; brings hands to mouth; pushes up on elbows
~6 months	Knows familiar people; laughs; mirror play	Takes turns making sounds; blows raspberries; squeals	Reaches for toys; mouths objects to explore	Rolls tummy-to-back; props on hands when sitting
~9 months	Shy with strangers; responds to name; peek-a-boo	“Mamama / babababa” sounds; lifts arms to be picked up	Looks for dropped/hidden things; bangs objects	Sits without support; rakes food; passes objects hand-to-hand
~12 months	Plays games like pat-a-cake	Waves bye-bye; says mama/dada; understands “no”	Puts items in a container; finds hidden things	Pulls to stand; cruises; pincer grasp; may take first steps

Newborn milestones: the first month (weeks 1–4)

In the first weeks your baby adjusts to life outside the womb. They begin to recognize your voice and find comfort in it — an early foundation for emotional security and language. Newborns focus best on objects about 8 to 14 inches away, the perfect distance for gazing at your face during feeds, which strengthens eye muscles and visual tracking. Movements are still uncoordinated, but you’ll notice an early preference for human contact, and by the end of the month many babies add soft cooing “ahh” sounds to their cries — the very beginning of communication.

Support it: hold your baby close, talk and sing during feeds, and offer short, daily tummy-time sessions to build neck strength. Feeding is a big part of these early weeks — if you’re finding your rhythm, our complete guide to bottle-feeding a newborn walks through paced feeding and comfort cues.

Months 1–2 milestones (weeks 5–8): the first smile

Around weeks 5–6, movements smooth out as muscle control develops, and many parents get the milestone they wait for: the first genuine social smile, bright eyes and all. Babies start associating sounds with objects (a rattle), prefer bright, colorful items, and — with tummy time — begin lifting the head higher off the floor. Per the CDC, by about two months most babies hold their head up on their tummy, move both arms and legs, make sounds other than crying, and smile when you smile at them.

Support it: respond to coos with your own “conversation,” offer high-contrast toys, and keep tummy time playful and short.

Months 2–3 milestones (weeks 9–12): discovering hands

Now your baby is more tuned in to sounds and faces, may coo back, stays awake for longer stretches, and makes a big cognitive leap: discovering their hands as objects they can control. That discovery sets up reaching, grasping, and self-soothing. You may also see the first laughs and more expressive babble.

Support it: name what your baby looks at, offer easy-to-grasp rattles, and protect daytime sleep so an alert, curious baby doesn’t become an overstimulated one. (A predictable rhythm helps — see our realistic guide to baby sleep.)

Months 3–4 milestones (weeks 13–16): reaching & coordination

Expression blossoms: laughing, babbling, and experimenting with sounds. Hand-eye coordination improves as your baby reaches for and grasps dangling, rattling toys. By about four months, most babies hold their head steady without support, push up on their elbows during tummy time, bring hands to the mouth, and coo to get and keep your attention.

Support it: offer play-gym toys at arm’s reach, and keep up tummy time to build the upper-body strength rolling and sitting will need.

Months 4–5 milestones (weeks 17–24): rolling & raspberries

Strength and curiosity surge. Many babies start rolling (often tummy-to-back first), push up on straight arms, and — socially — laugh, blow raspberries, take turns making sounds, and recognize familiar people. Everything goes in the mouth now; mouthing is how babies explore texture and shape, so safe, clean toys matter.

Support it: give floor time and room to roll, narrate your day to feed language, and keep mouthable toys clean. Around this window you may also notice readiness signs for solids — here’s how to spot them in our signs your baby is ready for solid foods guide.

Months 6–7 milestones (weeks 25–32): sitting up

The six-month mark is a major one. Per the CDC, by six months most babies roll from tummy to back, push up with straight arms, lean on their hands to support themselves when sitting, reach to grab a toy, put things in the mouth to explore, and close their lips to show they don’t want more food. Many are starting solids around now, sitting with support, and clearly enjoying back-and-forth “conversation.”

Support it: practice supported sitting, offer first foods responsively, and respect those “all done” cues — our starting-solids guide covers safe first foods.

Months 8–9 milestones (weeks 33–40): exploring & object permanence

Babies become busy explorers: sitting without support, passing objects hand-to-hand, raking up finger foods, and often beginning to scoot or crawl. Big cognitive gains arrive too — looking for dropped or hidden objects (the start of object permanence) and babbling “mamama” / “babababa.” Stranger awareness and separation reactions are normal and healthy. Note: 9 months is the AAP-recommended age for a general developmental screening at a well-child visit.

Support it: play peek-a-boo and hide-and-find games, offer safe self-feeding practice, and baby-proof for a newly mobile explorer.

Months 10–11 milestones (weeks 41–48): pulling up & problem-solving

Now you’ll see pulling to stand, cruising along furniture, more intentional gestures, and early problem-solving — finding hidden objects, fitting things into containers, and anticipating familiar routines. Communication grows more two-way, with gestures and sound combinations that clearly mean something.

Support it: create safe surfaces to pull up on, offer stacking cups and containers, and keep daily routines predictable so your baby can anticipate what comes next.

Month 12 milestones (weeks 49–52): standing, maybe walking

By the first birthday, many babies pull to stand, cruise, use a pincer grasp, wave bye-bye, say a word or two (mama/dada), understand “no,” and play games like pat-a-cake. Some take their first independent steps around now — but plenty of perfectly healthy babies walk later, anywhere up to around 18 months, so don’t worry if your one-year-old is still cruising. Most babies have roughly tripled their birth weight by their first birthday.

Support it: give safe space to cruise and stand, read together every day, and celebrate communication attempts.

How to support your baby’s development at home

You don’t need fancy gear — responsive, everyday interaction does the heavy lifting. A few high-value habits:

• Talk, sing, and narrate all day; this builds language long before first words.
• Daily tummy time from the newborn stage to build the strength behind rolling, sitting, and crawling.
• Floor play and safe exploration over screens or containers; movement drives motor and cognitive growth.
• Open-ended toys matched to the stage — high-contrast cards early, then rattles, stacking cups, and cause-and-effect play. QB’s Playmaze and the developmental ideas in our developmental toys for 6 months to 1 year guide are easy places to start.
• Predictable feeding and sleep rhythms, which give your baby the regulated, rested state where learning happens best.

When to talk to your pediatrician

Milestone ranges are wide, but reach out to your pediatrician if your baby misses several milestones for their age, loses a skill they once had, or anything about their development worries you — and don’t wait for the next scheduled visit if you’re concerned. Early action and developmental screening (recommended by the AAP around 9, 18, and 30 months) are the most reliable way to support healthy development. For premature babies, your provider will track progress using corrected age.

Frequently asked questions

What developmental milestones should my baby reach in the first year?

Across the year, most babies progress from social smiles (~2 months) to rolling and reaching (~6 months), sitting and babbling (~9 months), and pulling to stand, waving, and often first steps (~12 months), alongside steady language and cognitive growth. The CDC frames these as things most children (75%+) can do by each age, not a fixed schedule.

When do babies smile, roll, sit, crawl, and walk?

As a rough guide: social smile around 2 months, rolling around 4–6 months, sitting without support around 6–9 months, crawling around 8–10 months, and walking anywhere from about 9 to 18 months. The ranges are wide and overlapping, and reaching skills slightly earlier or later is normal.

Is it normal for my baby to hit milestones late?

Often, yes. Milestones describe what most babies do by a certain age, not the only normal timing. Many healthy babies reach some skills early and others later. What matters is steady overall progress; if several milestones are delayed or a skill is lost, check with your pediatrician.

When should I worry about a missed milestone and talk to a doctor?

Talk to your pediatrician if your baby misses several milestones for their age, loses a skill they previously had, or if anything about their development concerns you. You don’t need to wait for the next checkup — early action and developmental screening are the recommended path.

Do milestones happen on an exact weekly schedule?

No. Week-by-week framing is a helpful narrative, but real development unfolds in overlapping ranges, not precise weeks. Two healthy babies can reach the same milestone weeks apart. Use stages as a map and focus on direction of travel.

Do premature babies follow the same milestone timeline?

Premature babies are usually assessed by corrected age (age calculated from the due date rather than the birth date), so they may reach milestones later than the calendar suggests and still be right on track. Your pediatrician will guide expectations based on your baby’s history.

How can I support my baby’s development at home?

Talk, sing, and narrate constantly; do daily tummy time; give plenty of floor play and safe exploration; offer stage-appropriate, open-ended toys; and keep feeding and sleep rhythms predictable. Responsive, everyday interaction matters far more than special equipment.

Does how I feed my baby affect their development?

Feeding method (breast, bottle, or both) doesn’t set the milestone timeline, but responsive, calm feeding supports the bonding, regulation, and nutrition that healthy development depends on. Starting solids around six months, when readiness signs appear, also supports motor skills like self-feeding and pincer grasp.

Sources: CDC — Learn the Signs. Act Early. (Developmental Milestones); AAP / HealthyChildren.org — Ages & Stages: Baby; WHO — Child Growth Standards (motor development windows).

Medically reviewed by Dr. Collin Yang, MD. Last reviewed June 12, 2026.