Most babies start sleeping through the night between 3 and 6 months of age, though some don’t reach this milestone until closer to their first birthday. “Sleeping through the night” for an infant means at least six uninterrupted hours, not the eight or more adults typically expect. Your baby may still wake briefly during those hours but drift back to sleep without your help.
Two key factors determine when this happens: your baby’s stomach needs to be large enough to go several hours without a feeding, and their brain needs to develop the ability to settle back to sleep on their own. Both of these milestones unfold on their own timeline.
Why Newborns Can’t Sleep Long Stretches
A newborn’s stomach holds very little. In the first month through about three months, capacity tops out around 4 to 6 ounces. That small fuel tank empties quickly, which is why newborns wake every two to three hours around the clock. Between 3 and 6 months, stomach capacity grows to about 6 to 7 ounces, and by 6 to 9 months it reaches 7 to 8 ounces. As your baby can take in more calories during the day, the biological need for nighttime feeds gradually fades.
According to the Children’s Hospital of Philadelphia, most babies don’t begin sleeping six to eight hours without waking until they reach at least 3 months of age or weigh 12 to 13 pounds. That weight threshold reflects the point where a baby’s body can store enough energy to sustain a longer fast overnight. Some babies hit 12 pounds at 2 months, others not until 4 months, so the timing varies.
Breastfed vs. Formula-Fed Babies
Breastfed babies tend to wake more often at night than formula-fed babies. Breast milk digests faster than formula, so breastfed infants get hungry again sooner. A systematic review of the research confirmed that breastfed infants and their mothers experience more nighttime wake-ups. However, total sleep time across a full 24-hour period doesn’t actually differ between the two groups. Breastfed babies aren’t sleeping less overall; they’re just splitting their sleep into shorter chunks.
This means switching to formula purely for better sleep may not deliver the payoff parents expect. The extra wake-ups from breastfeeding tend to be brief, and the overall hours of sleep your baby gets will likely stay the same.
The 3-to-6-Month Window
Between 3 and 6 months, several things converge. Your baby’s stomach is bigger, their circadian rhythm (the internal clock that distinguishes day from night) is maturing, and their nervous system is developing the ability to self-soothe. Self-soothing is the skill that lets a baby wake slightly between sleep cycles and fall back asleep without crying for you. It’s the real difference between a baby who “sleeps through the night” and one who doesn’t.
Most babies begin developing self-soothing skills between 6 and 9 months. Before that age, they rely on you to help them settle. This is why many babies who seemed like great sleepers at 3 months suddenly start waking again at 4 or 5 months. They were sleeping through lighter sleep cycles as newborns, but as their sleep architecture matures around 4 months, they cycle through deeper and lighter stages more like adults do, and they haven’t yet learned to bridge those transitions on their own.
Sleep Regressions That Disrupt Progress
Just when you think you’ve turned a corner, your baby may start waking frequently again. These setbacks are called sleep regressions, and most babies experience at least one during their first year. The most well-known regression hits around 4 months, but regressions are less tied to a specific age and more tied to what your baby is going through at the time.
Common triggers include:
- New physical milestones. Babies who have just learned to roll over or pull themselves up often want to practice these skills at 2 a.m. instead of sleeping.
- Separation anxiety. This peaks around 9 months and can make your baby resist being alone in a crib.
- Illness. A cold, ear infection, or teething pain can disrupt sleep for days or weeks.
- Routine changes. Starting daycare, traveling, or even a shift in nap schedules can throw off nighttime sleep.
- Hunger from a growth spurt. Babies going through rapid growth may need extra calories temporarily, leading to more night waking.
Regressions typically last two to four weeks. They feel permanent in the moment, but they resolve as your baby adjusts to whatever developmental leap triggered them.
What You Can Do to Help
You can’t force a baby to sleep through the night before they’re physically and neurologically ready, but you can create conditions that support longer stretches of sleep as those abilities come online.
A consistent bedtime routine signals to your baby’s brain that sleep is coming. This doesn’t need to be elaborate: a feeding, a diaper change, a short book or song, then placing your baby down drowsy but awake. That last part matters because babies who fall asleep independently at bedtime are more likely to resettle on their own when they wake between sleep cycles overnight.
The AAP recommends keeping your baby’s sleep space in your room for at least the first 6 months, but in their own crib or bassinet rather than in your bed. The sleep surface should be firm and flat with no pillows, blankets, stuffed animals, or bumper pads. Always place your baby on their back. Offering a pacifier at bedtime can also help, as it’s associated with a lower risk of SIDS even if the pacifier falls out after your baby is asleep.
Once your baby starts showing signs of rolling over, usually around 3 to 4 months, stop swaddling. A sleep sack with open arms is a safe alternative that still provides the cozy feeling without restricting movement.
A Realistic Timeline
Here’s roughly what to expect, keeping in mind that every baby is different:
- 0 to 2 months: Sleep comes in 2-to-4-hour chunks around the clock. Night waking for feeds is biologically necessary.
- 3 to 4 months: Some babies begin sleeping one longer stretch of 4 to 6 hours. Many don’t, and that’s normal. The 4-month sleep regression can temporarily undo any progress.
- 5 to 6 months: A growing number of babies can manage 6 or more hours. Stomach capacity and circadian rhythms are more established. Self-soothing skills are starting to emerge.
- 6 to 9 months: This is when many babies consolidate nighttime sleep into longer blocks. Self-settling skills are developing, and caloric needs can increasingly be met during the day. Separation anxiety around 9 months may cause a temporary setback.
- 9 to 12 months: Most babies are capable of sleeping through the night by this point, though some still wake once for comfort or a quick feed.
If your baby is older than 6 months, eating well during the day, growing on track, and still waking multiple times a night, it’s often a habit-based pattern rather than a physical need. This is the age range where gentle sleep training approaches tend to be most effective, because your baby’s nervous system is mature enough to learn the skill of falling back to sleep independently. Babies younger than about 4 months generally aren’t developmentally ready for structured sleep training of any kind.