Most babies begin sleeping through the night somewhere between 4 and 9 months of age, though the timeline varies widely. What counts as “sleeping through” matters here: researchers define it as sleeping from roughly 10 p.m. to 6 a.m. without needing a parent’s help to fall back asleep. By that standard, some babies hit the milestone at 4 months, while about 28% still haven’t gotten there by their first birthday. Both ends of that range are normal.
What “Sleeping Through the Night” Actually Means
Every baby wakes briefly during the night. Adults do too. The difference is whether your baby can drift back to sleep on their own or needs you to step in. Researchers studying infant sleep use three benchmarks: sleeping from midnight to 5 a.m. (the loosest definition), sleeping 8 consecutive hours, and sleeping from 10 p.m. to 6 a.m., which lines up best with a family’s actual schedule. That last one, 10 p.m. to 6 a.m., is considered the most practical and developmentally meaningful measure.
So when your pediatrician or a parenting book says a baby “sleeps through the night,” they don’t mean the baby never stirs. They mean the baby wakes briefly between sleep cycles and settles back down without crying for you.
The Biology Behind the Timeline
A newborn’s internal clock barely exists. Babies aren’t born with the hormonal rhythms that tell the body it’s nighttime. The daily melatonin cycle, which signals drowsiness in the evening, typically appears around 12 weeks. The cortisol rhythm, which produces the alertness spike that helps you wake up in the morning, takes longer. It gradually develops from birth and stabilizes into an adult-like pattern between 6 and 9 months.
This is why the 4 to 6 month window is so pivotal. Before that point, your baby’s body doesn’t have the hormonal infrastructure to distinguish night from day in a reliable way. Once melatonin production kicks in and cortisol settles into a predictable morning peak, the biological foundation for consolidated nighttime sleep is in place. But biology alone isn’t enough. Your baby also needs to learn a skill: self-soothing.
When Self-Soothing Develops
Self-soothing is the ability to calm down after waking, without a parent rocking, feeding, or holding the baby back to sleep. It starts appearing in some infants between 4 and 6 months and tends to increase in frequency through the first birthday. But it’s not a switch that flips. Some babies pick it up quickly, others take much longer, and the variation is enormous.
Research tracking babies from birth to 12 months found that by one year, roughly 72% of infants were self-regulated sleepers who could manage nighttime wake-ups independently. The remaining 28% still needed parental help. Those non-self-regulated sleepers woke more often (about 11 times over a six-night period compared to 7 times for self-regulated sleepers) and had shorter stretches of uninterrupted sleep.
This doesn’t mean something is wrong with the 28%. Infant sleep development isn’t linear, and temperament plays a real role. Some babies are simply lighter sleepers or more sensitive to transitions between sleep cycles.
How Feeding Method Affects Night Waking
Breastfed babies wake more often at night than formula-fed babies. This is one of the most consistent findings across sleep research, and it’s partly because breast milk digests faster than formula, leading to more frequent hunger cues. Breastfeeding mothers also tend to feed more often overnight.
Here’s what’s interesting, though: despite waking more often, breastfed babies get the same total amount of sleep as formula-fed babies. The time spent awake during the night is also similar between the two groups. The perception that formula-fed babies are “better sleepers” is widespread, but the actual difference is in wake frequency, not in overall sleep quality or duration. If you’re breastfeeding and feeling pressure to switch to formula for better sleep, that tradeoff is smaller than it appears.
Sleep Cycles Are Shorter in Babies
Adults cycle through light sleep, deep sleep, and dream sleep in roughly 90-minute loops. Babies cycle much faster, and they spend less time in deep REM sleep. These shorter cycles create more opportunities for brief awakenings. Each time a baby transitions from one cycle to the next, there’s a chance they’ll wake fully instead of drifting into the next phase. This is normal infant neurology, not a sleep problem. As the brain matures through the first year, sleep cycles gradually lengthen and become more stable.
Why Sleep Gets Worse Before It Gets Better
Even babies who were sleeping well often hit rough patches. Parents commonly report disrupted sleep in 36% to 45% of infants between 4 and 12 months. These disruptions tend to cluster around developmental milestones.
The 4-month regression is one of the most noticeable. At this age, babies are becoming more socially aware, starting to roll over, and grabbing objects with purpose. They’re also transitioning to a more consolidated sleep schedule, which can temporarily make things worse. Many parents blame teething at this stage, but most babies don’t actually start teething until closer to 6 months. The drooling you see at 4 months is from salivary glands being stimulated by all the hand-to-mouth exploration.
Around 8 to 9 months, separation anxiety emerges. Babies at this age understand that you still exist when you leave the room, which is a cognitive leap forward but makes falling asleep alone harder. Teething is also genuinely underway by this point and can contribute to nighttime discomfort. Another disruption often hits around 12 months as babies begin walking and their brains are processing a flood of new motor information.
A Realistic Month-by-Month Picture
Newborns to 3 months sleep in short bursts around the clock with no real distinction between day and night. There is no expectation of sleeping through at this stage.
Between 3 and 4 months, melatonin production starts and you may notice your baby developing a preference for nighttime sleep. Some babies begin stretching their longest sleep period to 5 or 6 hours, but most still need at least one overnight feed.
From 4 to 6 months, self-soothing behaviors start to emerge and circadian rhythms are solidifying. This is when many families see the first real stretches of uninterrupted nighttime sleep. Some babies will meet that 10 p.m. to 6 a.m. benchmark here.
Between 6 and 9 months, the cortisol rhythm stabilizes into its mature morning-peak pattern. Babies who haven’t yet started sleeping through often do during this window, though regressions from teething or separation anxiety can interrupt progress.
By 12 months, the majority of babies (around 72%) are self-regulated sleepers. The rest are still working on it, and that’s within the normal range. Night waking at this age doesn’t indicate a developmental problem.
What You Can Actually Control
You can’t force a baby’s circadian rhythm to mature faster, but you can support the process. Exposing your baby to natural light during the day and keeping nighttime feedings dim and quiet helps reinforce the difference between day and night. Consistent bedtime routines give your baby cues that sleep is coming. Putting your baby down drowsy but awake, when they’re developmentally ready for it (usually around 4 to 6 months), gives them practice transitioning to sleep independently.
The single biggest factor, though, is your baby’s individual biology. Two babies born on the same day, fed the same way, in similar households, can have completely different sleep trajectories. If your baby isn’t sleeping through the night at 6 months while your friend’s baby has been doing it since 4 months, that gap is more about neurology and temperament than anything you’re doing wrong.