Most babies begin sleeping through the night somewhere between 3 and 6 months old, though the range is wide and “sleeping through the night” doesn’t mean what most new parents think it does. A baby who sleeps through the night still wakes up multiple times. The difference is that they can settle themselves back to sleep without your help. Understanding that distinction takes a lot of pressure off.
What “Sleeping Through the Night” Actually Means
New parents often picture an unbroken 10- or 12-hour stretch, but that’s not the clinical benchmark. Even adults wake briefly between sleep cycles and rarely remember it. Babies do the same. A baby considered a “good sleeper” is one who wakes frequently but can get back to sleep on their own, not one who never stirs for 10 hours straight.
In most pediatric research, sleeping through the night means a stretch of about 6 to 8 consecutive hours without needing a feeding or caregiver intervention. By that standard, many babies hit the milestone earlier than parents realize, because the baby is briefly waking and self-soothing without crying.
Why It Happens Between 3 and 6 Months
Two biological systems need to mature before a baby can sleep in long stretches: their internal clock and their stomach.
Babies aren’t born with a functioning circadian rhythm. The sleep hormone melatonin starts showing a clear day-night pattern around 8 weeks of age, with about 61% of daily production concentrated during nighttime hours. By 16 weeks (4 months), that rhythm stabilizes further and becomes less influenced by outside factors like the season in which the baby was born. This is why the 3- to 4-month mark is when many families first notice longer nighttime stretches emerging.
Stomach capacity plays an equally important role. A newborn’s stomach holds roughly 20 milliliters, which empties in about an hour. That tiny tank is why newborns need to eat around the clock. As the stomach grows over the first few months, babies can take in enough calories during a feeding to sustain them for longer stretches, eventually making it 6 or more hours without hunger waking them.
Breastfed vs. Formula-Fed Babies
You’ll 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 when researchers tracked overall sleep patterns through the first two years, fully breastfed infants actually logged longer total nighttime sleep at 6, 9, 12, and 24 months than formula-fed infants.
So breastfed babies wake more often but sleep more overall. Formula-fed babies may have fewer wake-ups, but that doesn’t translate into more total sleep. Neither feeding method is “better” for sleep in the long run. If you’re breastfeeding and your baby still wakes at 5 months for a feed, that’s biologically normal.
Why Some Babies Take Longer
Plenty of healthy babies don’t consistently sleep through the night until 9 or even 12 months. Several things can push the timeline out.
- Growth spurts temporarily increase caloric needs, adding an extra feeding or two at night even after weeks of solid sleep.
- New physical skills like rolling over, crawling, or pulling to a stand can disrupt sleep. Babies sometimes wake up and want to practice their new abilities instead of settling back down.
- Separation anxiety typically peaks around 8 to 10 months and can cause a baby who previously self-soothed to cry when they wake and realize you’re not there.
- Illness and teething are straightforward disruptors. A cold or emerging teeth can undo weeks of progress overnight.
These disruptions are sometimes called “sleep regressions,” but that label can be misleading. They’re less about a specific age and more about what the baby is going through developmentally. A consistent sleep pattern usually begins forming around 4 months, and any of the factors above can temporarily interrupt it. Most regressions last one to three weeks before the baby returns to their previous pattern.
What You Can Do to Help
You can’t force a baby to sleep through the night before they’re biologically ready, but you can set up conditions that make it easier once they are.
Consistent bedtime routines matter more than the specific activities in them. A predictable sequence (bath, feeding, dim lights, same sleep space) helps signal to the baby’s developing circadian system that nighttime is coming. Putting a baby down drowsy but still awake gives them a chance to practice falling asleep independently, which is the core skill behind sleeping through the night.
If your baby is older than 4 to 6 months, still waking frequently, and you want to try a more structured approach, graduated sleep training is one option. The basic idea is to let the baby fuss for increasing intervals before briefly reassuring them, helping them learn to self-soothe. Most families who use this method see improvement within about a week. It’s not the only approach, and it’s not required. Many babies figure it out on their own with time.
The Wide Range of Normal
By 6 months, roughly half of babies can sleep a 6- to 8-hour stretch most nights. By 9 months, the majority can. But a significant number of perfectly healthy babies still wake once or twice a night well into their first year, and some into the second year. The variation is enormous, and it tracks more closely with individual temperament than with anything parents are doing right or wrong.
If your 4-month-old is already sleeping 7-hour stretches, that’s great. If your 8-month-old still wakes twice, that’s also within the range of normal. The trend matters more than any single night. As long as nighttime stretches are gradually getting longer over the months, sleep development is moving in the right direction.