Sleep

When do babies sleep through the night?

The two definitions of "through the night"

First issue with this question: the answer depends on whose definition you're using.

Pediatric definition. In peer-reviewed sleep studies, "sleeping through the night" means a 5- or 6-hour uninterrupted stretch — typically from around midnight to 5 a.m. By that bar, most healthy babies hit it sometime between 3 and 6 months.

Parent definition. What most parents mean by "sleeping through the night" is closer to 11 hours uninterrupted, from a 7 p.m. bedtime to a 6 a.m. wake-up. That bar is much higher and arrives later. The median age for this pattern is 9-12 months, with significant variation either side. Some babies hit it at 6 months; some don't reliably hit it until 18-24 months. Both ends are within normal.

Knowing which definition you're holding yourself (and your baby) to is the first useful move. "My six-month-old still wakes once at 3 a.m." is not a problem. "My six-month-old wakes every 90 minutes" is a different conversation.

What the data actually says

A few numbers from the largest infant-sleep cohort studies (Henderson et al. 2010, Mindell et al. 2016):

• At 1 month: ~25% of babies do a 5-hour stretch
• At 3 months: ~50% do a 6-hour stretch
• At 6 months: ~60% do a 6-hour stretch; ~30% do an 8-hour stretch
• At 9 months: ~70% do an 8-hour stretch
• At 12 months: ~80% do an 8-hour stretch
• At 24 months: nearly all neurotypical babies are doing 10-12 hour overnight stretches

What changes between birth and "through the night"

Three biological things have to happen for a baby to consolidate night sleep:

1. Stomach size grows. Newborn stomachs hold roughly 1-2 ounces. They cannot physically take in enough calories at one feed to last 6+ hours. By 4-5 months, stomach capacity has grown enough that it's mechanically possible to skip an overnight feed. 2. Circadian rhythm develops. Newborns don't distinguish day from night — their melatonin cycle isn't established. Most babies develop a recognizable day-night pattern between 8-12 weeks. Once melatonin is rhythmically released at night, sleep gets deeper and longer. 3. Sleep cycle architecture matures. Adult sleep cycles run ~90 minutes; newborn cycles run ~50-60 minutes, and babies wake briefly between cycles. "Sleeping through" really means "learning to bridge sleep cycles without crying." This skill develops over months 4-12.

None of this is teachable. Sleep training methods (cry-it-out, Ferber, etc.) work on the third item — bridging cycles — but only after the first two have happened biologically. Trying to sleep-train at 8 weeks doesn't work because the underlying biology hasn't matured.

What changes the timeline

Individual variation is huge, but a few factors push earlier or later:

Earlier-than-average:

• Formula-fed babies (formula digests slower; longer stretches between feeds)
• Larger babies / higher percentile for weight
• Babies with calm temperament / low "alertness" trait
• Consistent bedtime routine starting early

• Premature babies (adjust for prematurity — a 6-month-old born 2 months early sleeps like a 4-month-old)
• Reflux, colic, or any chronic discomfort
• Frequent ear infections in months 6-12
• Teething (causes regressions but rarely permanent shifts)
• Highly intense / high-needs temperament
• Cosleeping (slightly later — frequent close-by feeds means frequent waking)

Sleep regressions are real

Even after a baby has "slept through," expect regressions at the standard developmental milestones:

• 4-month regression — the major one; biology shifts to adult-style sleep cycles
• 8-10 month regression — separation anxiety + crawling/standing milestones
• 12-month regression — walking + language development
• 18-month regression — molars, language explosion, autonomy

What couples can do (and what doesn't help)

The couple-impact of broken sleep is the under-discussed half of this question. Things that help:

1. Trade off. Whoever doesn't have the next morning's first responsibility takes the night feed; the other gets uninterrupted sleep. Even one full night's rest twice a week dramatically changes both partners' functioning. 2. Don't compare your baby's sleep to other people's babies. This is the fastest route to feeling like a failure as a parent. Variation is enormous and other people lie about it (kindly, but they do). 3. Cap the awake-baby-handling at one parent at a time after midnight. No reason for both partners to be awake at 3 a.m. unless one of you genuinely needs the other's help. 4. Don't sleep-train before 16 weeks adjusted. The biology isn't there. You'll burn yourselves out trying to teach a skill the baby doesn't yet have the wiring for. 5. Do consider sleep-training at 5-7 months if both partners are aligned and the baby is otherwise healthy. There's strong evidence (Gradisar 2016) that brief, structured sleep training in this window doesn't harm attachment and substantially improves both child and parent sleep.

Things that don't help: comparing your baby to your friend's baby, blaming yourselves, blaming each other, or believing the next product/method/expert will be the magic answer. Sleep is mostly biology with a small training component, and the biology arrives on its own schedule.

Sources

• AAP — Sleep and Your Baby
• Mindell et al. — Cross-Cultural Differences in Infant Sleep
• Henderson et al. — Sleeping Through the Night Defined
• Gradisar et al. — Behavioral Interventions for Infant Sleep

Related questions

• Is it OK to let baby cry it out?
• What temperature should the baby's room be?

We cite the sources we relied on. This page is for general orientation only and does not replace medical advice from your pediatrician. If your baby has any specific feeding, sleep, or safety concern, always check with a clinician who knows your kid.