4-Month-Old Milestones: Development, Growth, Speech, and Sleep

Four months in, your baby is a different creature than the newborn you brought home. They hold their head up on their own, they chuckle when you make a silly face, and they've started grabbing at anything that dangles near their hands. There's a personality in there now.

Four months is also a checkpoint pediatricians pay attention to, with a well visit, a full milestone review, and a shift in the whole day starting to take shape. Here's what most 4-month-olds are doing, grouped the way your pediatrician thinks about it, with the numbers and the sources behind them.

What should a 4-month-old be doing?

Most 4-month-olds hold their head steady when held upright, push up onto their elbows during tummy time, coo and make sounds back at you, reach and swing at toys, and bring their hands to their mouth.¹ The CDC updated its milestone checklists in 2022 so each listed skill is something about 75% of babies can do by that age, not the average.² If your baby is doing most of these, they're right on track, and a wide spread of timing is still normal.

Pediatricians watch four rough tracks maturing at the same time. Here's each one.

Movement and physical development

Steady head control. Held upright, a 4-month-old keeps their head up without it bobbing or needing support.¹ This is the foundation everything else is built on, including sitting later.

Pushing up on forearms. During tummy time your baby now props on their elbows and lifts their chest, taking in the room instead of face-planting into the mat.¹

Swinging at toys. Held over a play gym, babies this age swat and swing an arm toward dangling toys.¹ Aim is rough and misses are frequent, which is exactly how hand-eye coordination gets built.

Bearing weight through the legs. Many 4-month-olds push down with their legs when you hold them standing on your lap. Some 4-month-olds also start rolling from tummy to back around now, though the CDC lists reliable rolling a little later.³

Once rolling shows up, two safety notes. Stop swaddling at the very first sign of rolling, since a swaddled baby who flips to their stomach can't push up or turn their head to clear their airway.⁵ And glance around the floor and changing table, because a baby who can roll can roll off an edge in the second you look away.

Hands and fine motor skills

Holding a toy. Put a rattle in your baby's hand and they'll grip it now, rather than letting it drop the way a newborn would.¹

Hands to the mouth. Bringing both hands (and whatever they're holding) to the mouth is how a 4-month-old explores, and the CDC lists it as a normal milestone, not a habit to break.¹

Studying their own hands. Babies this age discover they have hands and will lie there turning them over, watching their fingers with real focus.¹ It looks like nothing, but it's early cause-and-effect learning.

Speech and language

Cooing. Long open vowel sounds ("oooo," "aahh") are the soundtrack of four months.¹ This is the raw material that turns into babble in a couple of months.

Answering back. Your baby makes a sound, you respond, and they make another sound in return.¹ That turn-taking is the scaffolding real conversation is built on later.⁴

Turning toward your voice. A 4-month-old turns their head toward where your voice is coming from.¹ It's a sign hearing and sound-location are working the way they should.

Social and emotional

Smiling to get your attention. By four months the social smile is deliberate. Your baby smiles on their own to pull you in, not just in response to yours.¹

Chuckling. Expect chuckles when you try to make them laugh, a step short of the full belly laugh that arrives a bit later.¹

Working to keep you engaged. A 4-month-old will look at you, move, or make sounds specifically to get or keep your attention.¹ They've figured out that you respond, and they like it.

How much sleep does a 4-month-old need?

About 14.5 hours in 24, usually around 10 at night and 4.5 across four naps.⁶ Wake windows run roughly 1.5 to 2.3 hours, shortest before the first nap and a touch shorter again before bed.

Four months is also when the well-known sleep regression hits, and it isn't really a regression. Your baby's sleep architecture is maturing into adult-like stages, which means more brief arousals between cycles until they learn to link them. We break the whole thing down, with a sample day and what actually helps, in our 4-month-old sleep schedule post, and the numbers for every age live in our wake windows chart.

Feeding a 4-month-old: milk now, solids soon

Breast milk or formula is still your baby's entire diet at four months, and it should stay that way for a few more weeks. The AAP recommends starting solids around 6 months, once the readiness signs are clearly there, not on a calendar date.⁷

The readiness signs worth watching for over the next couple of months: steady head control, sitting upright with support, real interest in your food (leaning in, watching your fork), and the fading of the tongue-thrust reflex that pushes a spoon back out.⁷ Some 4-month-olds show a few of these early, but most aren't ready yet, and there's no benefit to rushing.

If your baby has severe eczema or an egg allergy, this is the age to talk with your pediatrician about introducing peanut early rather than waiting. The LEAP trial found that regularly feeding peanut to high-risk infants from 4 to 11 months cut their chance of peanut allergy by roughly 80% by age 5.⁸ National guidelines now recommend introducing peanut (in an age-appropriate form, never whole nuts) for these babies as early as 4 to 6 months, with a doctor's guidance.⁹ For most babies without those risk factors, allergen introduction can wait until solids begin around six months.

Our feeding guide has milk amounts and frequencies broken out by age.

Growth at 4 months

Weight gain is still quick in the first half of the year, though it's about to slow. This month most babies add somewhere around 1 to 1.25 pounds and grow roughly half to three-quarters of an inch. Many babies double their birth weight somewhere around 4 to 5 months, so if the scale has climbed fast, that's expected.

Your pediatrician will plot height, weight, and head circumference against the WHO growth standards at the 4-month well visit.¹¹ They're watching the curve, not a single number. A baby who has followed the 20th percentile since birth and keeps following it is growing exactly as they should.

4-month milestone checklist

Development is a range, not a schedule, and not every baby ticks every box in the same week. Most 4-month-olds can:

• Hold their head steady without support when held upright
• Push up onto their elbows during tummy time
• Hold a toy you place in their hand
• Swing an arm at a dangling toy
• Bring their hands to their mouth
• Look at their own hands with interest
• Make cooing sounds ("oooo," "aahh")
• Make sounds back when you talk to them
• Turn their head toward your voice
• Smile on their own to get your attention
• Chuckle when you try to make them laugh

4-month red flags: when to call the doctor

Every baby is on their own clock, but a few signs at four months are worth raising with your pediatrician. Check in if your baby¹:

• Doesn't watch things as they move
• Doesn't smile at people
• Can't hold their head steady
• Doesn't coo or make any sounds
• Doesn't bring things to their mouth
• Doesn't push down with their legs when their feet are on a hard surface
• Has trouble moving one or both eyes in all directions
• Loses skills they used to have

No single item on its own means something is wrong, and you know your baby better than any list. If something feels off, the "act early" move is to ask sooner rather than wait and see.²

Two ways to support development at 4 months

Talk and pause. Narrate what you're doing, then leave a beat of silence for your baby to "answer." Those little cooing exchanges are early conversation practice, and the back-and-forth matters more than the words.⁴

Give tummy time a reason. Put a favorite toy or a mirror just past your baby's hands during floor time. Reaching and pushing up to see it builds the neck, shoulder, and core strength behind rolling and, later, sitting.

A quick note on teething, since it often gets blamed around now: some babies do get their first tooth as early as four months, but the average is closer to six, and drool alone at this age is usually just drool.¹⁰ If a hard little ridge shows up on the lower gum, that's the real thing.

nappi tracks feeds, sleep, and milestones in one place, so the 4-month well visit becomes a matter of glancing at what actually happened instead of reconstructing it from memory.

Frequently Asked Questions

Should my 4-month-old be rolling over yet?

Some are, some aren't, and both are fine. The CDC lists reliable rolling a bit after four months.³ What matters more right now is steady head control and pushing up on the forearms, which are the strength that rolling grows out of. If your baby has those, rolling usually isn't far off.

Can I start solids at 4 months?

Usually not yet. The AAP recommends waiting until around 6 months and, more importantly, until your baby shows the readiness signs: steady head control, sitting with support, interest in food, and a faded tongue-thrust reflex.⁷ A few babies are ready between 4 and 6 months, but that's a call to make with your pediatrician, not on a birthday.

Why did my 4-month-old suddenly stop sleeping?

That's the 4-month sleep regression, and it's a permanent upgrade to how your baby's brain organizes sleep, not a step backward. More brief wake-ups between cycles are normal until they learn to connect them. Our 4-month-old sleep schedule post walks through what helps.

Is my 4-month-old teething?

Maybe, but probably not yet. The first tooth usually appears around six months, with a wide range that starts near four.¹⁰ Drooling, chewing on hands, and fussiness are common at four months whether or not a tooth is on the way. A firm ridge on the gum is the clearer sign.

When should my 4-month-old have their first laugh?

Chuckles are typical right at four months, and full belly laughs tend to follow over the next month or two.¹ If your baby smiles, coos, and works to keep your attention but hasn't laughed out loud yet, that's within the normal spread.