Newborn Week-by-Week Guide
The first 12 weeks — also called the fourth trimester — broken down one week at a time. What your baby is doing. How much they're feeding and sleeping. What your body is going through. When to call the pediatrician. What's actually normal.
How old is your baby in weeks?
Use the Wake Windows Calculator to find the right wake windows for any newborn week and prevent overtiredness — the #1 cause of short naps in the fourth trimester.
Open the calculator →What "the fourth trimester" actually means
Coined by pediatrician Harvey Karp, "the fourth trimester" refers to the first 12 weeks after birth — a developmental period when newborns are still adjusting to life outside the womb, and parents are recovering physically and emotionally from delivery. Newborns can't yet regulate their own body temperature, sleep cycles, or feeding rhythms. They need to be held, fed on cue, and kept close. This isn't spoiling them; this is meeting their biological needs.
For parents, the fourth trimester is the hardest stretch of early parenthood for most. Sleep deprivation, hormonal shifts, identity changes, physical recovery, and the relentless demand of caring for a newborn all collide. The goal of this guide is to tell you what to expect each week — what's normal, what's worth calling about, and how to survive — so you can stop Googling at 2 AM and get some rest.
Every baby is different. The ranges in this guide reflect typical newborns; outliers in either direction can still be healthy. When in doubt, call your pediatrician — they would much rather you call than not.
The first month (weeks 1–4)
Pure survival. Feeds every 2–3 hours around the clock, day/night confusion at its worst, your body in the thick of recovery, possible baby blues. Cord stump falls off. First pediatric visits at days 3–5 and at 2 weeks.
The middle stretch (weeks 5–8)
Social smiles emerge. Witching hour peaks. The 6-week postpartum visit lands in this stretch. By week 8, the 2-month pediatric visit and first vaccine round. You start to feel like a person again — sometimes.
End of the fourth trimester (weeks 9–12)
Longer sleep stretches. Reliable smiles and brief laughs. Return-to-work for many. Sleep training becomes an option (typically at 14–16 weeks). Your body's recovery is mostly complete; your mental health journey continues.
Related guides
Newborn guide — the full newborn cluster (sleep, feeding, safety, the 5 S's, witching hour, and more).
Fourth trimester survival guide — practical survival tactics, what to delegate, what to lower standards on.
Pregnancy week-by-week (40 weeks) — the prenatal version of this guide.
Wake Windows Calculator — the most-used tool for fourth-trimester sleep.
Bottle Feeding Calculator — how much milk by age and weight.