“Is he sleeping through yet?”

It’s one of the most common questions new parents face. And there’s usually a subtext: if he’s not, when will he be? And what are you doing about it?

The question carries an implicit assumption — that sleeping through the night is a normal, achievable milestone that babies should reach by some point in early infancy. The evidence doesn’t quite support that assumption.

What does “sleeping through” actually mean?

Before examining the research, it’s worth asking what “sleeping through the night” even means. The definition varies — sometimes considerably.

In many studies, “sleeping through” is defined as a continuous stretch of 5–6 hours, not 8 or 12. A baby who wakes at 10pm and next at 3am is technically “sleeping through” by this definition, even though they’re up in the early hours.

In day-to-day conversation, most parents mean something more like 7pm to 7am — a 12-hour stretch with no waking. That’s a different thing entirely.

What the research shows

A significant systematic review of normal infant sleep found substantial variation in when consolidation occurs [1]. Some findings:

  • At 3 months, many babies still wake 1–3 times overnight
  • At 6 months, frequent night waking remains common — a majority of infants still do not consistently meet even the 5-hour definition of “sleeping through”
  • At 12 months, night waking remains normal for a substantial minority of infants
  • Many children continue to wake at night into the toddler years

A Canadian cohort study following over 300 infants found that at 12 months, 62% of babies were not consistently sleeping 8 hours, and around a quarter were not sleeping 5 hours without waking [2]. At 24 months, a meaningful proportion still were not.

These are not outliers. This is normal variation.

Why the myth persists

If the evidence shows such wide variation, why is the “sleeping through by 4 months” expectation so entrenched?

A few reasons:

Selection bias in social settings. Parents whose babies sleep well mention it. Parents whose babies don’t sleep well often don’t mention it — because of shame, fatigue, or the sense that it’s their own fault. This creates a distorted perception of what’s common.

Cultural and commercial pressure. There is a large industry built around “fixing” baby sleep. Books, programmes, apps, consultants — all of which create or amplify the expectation that sleeping through is achievable and necessary. The commercial interest in this expectation is significant.

A genuinely recent phenomenon. The expectation that babies should sleep through the night — alone, in a cot, from early infancy — is culturally and historically unusual. Research on cross-cultural infant sleep shows that in many cultures, extended night feeding, co-sleeping, and infant waking well into toddlerhood are norms, not problems [3, 4]. The Western expectation is not a universal standard.

The cost of the expectation

The “sleeping through” milestone creates pressure that has real costs.

Parents compare their babies’ sleep to a standard that doesn’t reflect the actual distribution of normal infant sleep. When their baby doesn’t meet the standard, the blame often falls on the parents — on what they’re doing, or failing to do.

This is not benign. Research on postpartum mood consistently shows that parental expectations about infant sleep play a role in distress: it’s not just the waking itself, but the gap between expectation and reality that contributes to feeling overwhelmed [2].

An accurate expectation — that frequent night waking is normal, that “sleeping through” is a gradual and variable achievement, and that many children won’t consistently manage it before 18–24 months — doesn’t fix the exhaustion. But it does remove some of the shame that makes it harder.

What sleeping through actually looks like

Sleep consolidation is a gradual process, not a switch that flips. Most babies don’t go from frequent waking to 12-hour nights; they go from very frequent waking to slightly less frequent waking, then to occasional waking, then — eventually, and on their own timetable — to nights that look more like the cultural expectation.

The timeline varies. It is influenced by temperament, feeding method, developmental stage, and factors that aren’t well understood. It is not reliably predicted by what parents do or don’t do in the early months.

If your baby isn’t sleeping through by 4 months, 6 months, or even 12 months — that’s a wide range of normal. You are not alone, and you haven’t done something wrong. The same commercial pressure that drives the sleeping-through expectation also underpins the sleep regression narrative — both rely on a predictability that the evidence doesn’t support.

References below.