← Back to your baby's forecast

Waking up to the world: smiles, and the 4-month sleep regression (weeks 8 to 17)

Window 2 of the Fussy Phase Forecast · Last verified: July 7, 2026

The short answer: this is the window where your baby starts giving back: real smiles aimed at you, little “conversations” of coos, the first almost-laughs. Rough patches around weeks 8 and 12 are common, sleep can get strange, and none of it means something is wrong.

Your baby discovers you are interesting

Somewhere in these weeks, the fog lifts a little. The baby who mostly ate, cried, and slept starts looking for you on purpose. By 4 months, most babies smile on their own just to get your attention (CDC milestone checklist). Not a reflex, not gas. A real “hey, you, look at me.”

The sounds start too. Cooing (“oooo”, “aahh”), and the beginnings of turn-taking: you talk, they answer with a sound, you answer back. That loop is not just adorable, it is on the CDC’s official list of things most babies do by 4 months: “makes sounds back when you talk to him.” So those silly one-sided chats you have while changing a nappy? That is development work. Keep going.

The rough patches around weeks 8 and 12

The same 1992 study we mentioned in the last article, the one that followed 15 mothers and babies week by week, noticed extra-fussy patches around week 8 and again around week 12: more crying, more clinging, and for some babies, lighter sleep and fussier feeds for a few days (the research, reviewed here).

The honest footnote, as always: when other researchers tried to confirm those exact weeks, they could not. The rough patches are real, the calendar is not strict, and your baby may hit them earlier, later, or barely at all. If week 10 is your hard week, your baby did not miss a memo.

One practical comfort: if you read our first article, you know crying overall peaks around 6 to 8 weeks and then falls week by week (NHS). So even with a fussy patch around week 8 or 12, the background noise is heading down.

About that “4-month sleep regression” you keep hearing about

Search the internet and you will find the 4-month sleep regression described as an unavoidable event, almost with a date and time. Here is what official guidance actually says. The NHS does not use the term at all. What it does say: all babies change their sleep patterns, every baby’s pattern is different, and growth spurts, teething, and illness can all shake sleep up (NHS: Helping your baby to sleep).

The same NHS page offers a realistic picture for 3 to 6 months: some babies start sleeping 5 to 8 hours or longer at night. Some. Not all. If yours is not one of them yet, that is inside normal, not behind schedule.

What can help, per the NHS:

• Teach day and night from early on: days bright and noisy, nights dark, quiet, and boring (feed, change only if needed, no playing)
• A simple, repeatable bedtime routine: bath, fresh nappy, dim lights, story or lullaby, goodnight kiss
• Keep your baby’s sleep space in your room for at least the first 6 months; it lowers the risk of sudden infant death syndrome
• Share the night shift if you can, and sleep when the baby sleeps, even if the house is a mess

What most babies do by 4 months

From the CDC’s 2022 checklists, built on what at least 75 percent of babies actually do (CDC, science behind it in Zubler et al., Pediatrics 2022):

• Smiles on their own to get your attention
• Chuckles (not yet a full laugh) when you try to make them laugh
• Looks at you, moves, or makes sounds to get or keep your attention
• Coos (“oooo”, “aahh”) and makes sounds back when you talk
• Turns their head toward the sound of your voice
• Opens their mouth when hungry and seeing the breast or bottle
• Looks at their own hands with interest (hands are fascinating, apparently)
• Holds their head steady without support when you hold them
• Holds a toy you put in their hand, and swings an arm at toys
• Brings hands to mouth, and pushes up onto elbows when on tummy

If your baby was born early, count from the due date, not the birth date. Development follows the adjusted age, and so does our forecast.

When to call your pediatrician

The CDC’s rule, plain and simple: if your baby is missing one or more of these milestones by 4 months, or has lost skills they once had, do not wait and see. Talk with the doctor and ask about developmental screening.

And the rule we repeat everywhere: your own concern is reason enough to call. No checklist knows your baby better than you do.

Keep reading

• Previous window: Weeks 0 to 8: settling in
• Next window: Weeks 17 to 26: grabbing everything
• How much sleep does a baby actually need?

Sources

• CDC: Milestone checklists, 2022 revision
• Zubler et al., “Evidence-informed milestones for developmental surveillance tools”, Pediatrics 2022
• NHS: Helping your baby to sleep (page last reviewed January 2025)
• NHS Black Country: Crying baby, the normal crying curve
• van de Rijt-Plooij & Plooij (1992) and follow-up research, KNAW review

Peanutbean provides general information for educational purposes only. It is not medical advice. Every baby develops at their own pace. Always talk to your pediatrician about your child’s health.