Most babies begin sleeping through the night somewhere between 3 and 6 months old, though what “sleeping through the night” actually means surprises many parents. Pediatricians don’t define it as 10 or 12 uninterrupted hours. A baby who sleeps through the night is one who wakes briefly but falls back to sleep on their own, not one who never stirs at all.
What “Sleeping Through the Night” Really Means
A stretch of 6 to 8 consecutive hours is the practical threshold most pediatric sleep experts use. For a baby who goes down at 7 p.m., that could mean waking at 1 or 2 a.m. for a feed and then sleeping again until morning. That counts. Many parents feel like failures because their 5-month-old still wakes once, when in reality that pattern is completely normal and on track.
The key shift isn’t that babies stop waking up. It’s that they develop the ability to resettle themselves after brief awakenings. Every human, adult or infant, cycles through lighter sleep stages multiple times per night. Babies who “sleep through” have simply learned to drift back without needing a parent to intervene.
The Biology Behind the Timeline
Two things need to mature before a baby can consolidate long stretches of nighttime sleep: their internal clock and their stomach.
Babies aren’t born with a functioning circadian rhythm. Their brains begin producing melatonin, the hormone that signals nighttime drowsiness, at around 8 weeks of age. By that point, infants already show a pattern of higher melatonin output during dark hours. By 3 to 4 months, this internal clock is strong enough to start distinguishing day from night in a meaningful way, which is why the 3-month mark is when many families notice the first longer stretches of sleep appearing.
Stomach capacity is the other piece. A newborn’s stomach holds roughly 20 milliliters, about four teaspoons. At that size, babies genuinely need to eat every one to two hours. By 3 to 4 months the stomach has grown enough to hold a larger feeding, and many babies can go 5 to 6 hours without calories. By 6 months, most healthy, normally growing babies no longer need nighttime feedings for nutritional reasons, though some pediatricians recommend continuing a night feed longer depending on the baby’s weight gain.
How Feeding Method Affects Sleep
Parents often hear that formula-fed babies sleep through the night sooner. The reality is more nuanced. Breastfed babies do wake more often between 6 and 12 months, likely because breast milk digests faster than formula. But research tracking sleep patterns over the first two years found that fully breastfed infants actually logged longer total night sleep and longer total sleep overall than formula-fed infants. The breastfed babies woke more frequently, but they also fell back to sleep more quickly, resulting in more sleep by the end of the night.
Partially breastfed babies, those getting a mix of breast milk and formula, slept about the same as fully breastfed babies. So supplementing with a bottle of formula before bed, a common strategy, doesn’t appear to make a significant difference in total sleep duration.
A Realistic Month-by-Month Picture
At 2 months, you might see one longer stretch of 4 to 5 hours emerge, usually in the first half of the night. This is the earliest sign that the circadian rhythm is kicking in. Don’t expect consistency yet.
Between 3 and 4 months, many babies begin sleeping 5 to 6 hour stretches. This is also when nap patterns start to organize into something more predictable. Total sleep needs at this age are 12 to 16 hours per 24-hour period, including naps.
By 6 months, roughly half of babies can manage a 6 to 8 hour stretch without a feeding. Some do even longer. Others, perfectly healthy ones, still wake once or twice. Both are normal.
Between 9 and 12 months, the majority of babies are capable of sleeping 10 to 12 hours overnight with zero or one feeding. “Capable” is the important word here, because several things can temporarily derail sleep right when you think you’ve turned a corner.
Why Sleep Gets Worse Before It Gets Better
Sleep regressions are periods of worse sleep lasting two to four weeks, and they tend to cluster around developmental leaps rather than specific ages. The triggers are predictable: growth spurts that create extra hunger, new motor skills the baby wants to practice (rolling, crawling, pulling to stand), illness, teething pain, travel or routine changes, and separation anxiety.
Separation anxiety peaks around 9 months and can turn a baby who was sleeping beautifully into one who screams the moment you leave the room. Babies learning to walk often have disrupted sleep as well. Research on infant motor development found that babies actively acquiring walking skills had measurably worse sleep than other babies their age. Their brains appear to process and consolidate new movement patterns during sleep, which increases restlessness and night waking.
These regressions feel like setbacks, but they’re signs of normal development. They pass. The sleep skills your baby had before the regression are still there, and most babies return to their previous pattern within a few weeks.
What You Can Do to Help the Process
You can’t force a baby’s circadian rhythm to mature faster, but you can support it. Expose your baby to natural light during the day, especially in the morning. Keep nighttime feedings and diaper changes dim and boring. By 3 to 4 months, a consistent bedtime routine (even a short one: bath, book, feed, bed) helps signal that long sleep is coming.
Putting your baby down drowsy but awake is the single habit most strongly linked to self-settling. Babies who always fall asleep while being rocked or fed tend to need that same intervention at every brief nighttime waking. Babies who practice falling asleep in their crib are more likely to resettle on their own when they stir at 2 a.m.
If your baby is still waking frequently at 6 months and you’re exhausted, that’s a reasonable time to consider more structured sleep training approaches. Multiple methods exist on a spectrum from very gradual to more direct, and the evidence consistently shows they’re safe and effective when started at an appropriate age. But plenty of families choose not to sleep train and still find that their baby’s sleep consolidates naturally between 6 and 12 months as the brain matures.
When Later Is Still Normal
Some perfectly healthy babies don’t reliably sleep through the night until 12 months or beyond. This is more common in breastfed babies, babies with reflux, and babies with a more sensitive temperament. It doesn’t mean something is wrong, and it doesn’t mean you’ve created bad habits. Sleep consolidation has a wide range of normal, and comparing your baby to a friend’s baby who slept 12 hours at 8 weeks tells you almost nothing useful. That friend’s baby is an outlier, not the standard.