Why is my 4-month-old suddenly waking up more at night?

Around four months a baby's sleep matures from mostly deep sleep into adult-like cycles that move through lighter and deeper phases. During the lighter phases babies wake more easily, which can mean more night waking for a while. It is a normal sign of healthy development, not a step backwards.

How long does the 4-month sleep regression last?

Most sleep regressions settle within a couple of weeks. How calmly and consistently caregivers respond can influence how long it lasts. If it drags on well beyond that, or something does not seem right, check in with your doctor.

What helps during the 4-month sleep regression?

A consistent, calming bedtime routine, avoiding overtiredness with an age-appropriate (often earlier) bedtime, plenty of daytime light and activity, giving your baby a chance to settle themselves, and steady, reassuring responses. Keep following safe-sleep rules throughout.

Sleep guide → 4-month regression

The 4-month sleep regression: why it happens and what helps

If your baby was finally sleeping in longer stretches and has suddenly started waking again, you're not doing anything wrong — and your baby isn't either. The so-called 4-month sleep regression is really a sign of normal brain development. Here's what's going on, and the calm, evidence-based things that help, drawn from Cleveland Clinic and the Sleep Foundation.

Please read first

This is general education, not medical advice, and can't replace your own doctor, pediatrician, GP or health visitor. If your baby seems unwell, is feeding poorly, or anything worries you, contact them. In an emergency, call your local emergency number.

What it actually is

Despite the name, a "regression" isn't your baby going backwards. It's a developmental leap that temporarily disrupts sleep. As Cleveland Clinic explains, early on babies spend more of their time in deep sleep; as they grow, their sleep starts to cycle through lighter and deeper phases — much more like adult sleep. Adjusting to those lighter phases means babies surface more easily and can wake for a bit between cycles. The result is more night waking, for a while.

Why it happens around 4 months

Two things are maturing at once. First, those sleep cycles: in the first months, sleep is split fairly evenly between active (REM) and quiet (non-REM) sleep, and over time the pattern reorganises into more structured, adult-like cycles. Second, the body clock — the circadian rhythm — is developing roughly between two and six months, helped along by daylight, so babies gradually start to consolidate more sleep at night. While all of this is settling into place, sleep can be unsettled. It's a transitional phase, not a permanent change.

Signs you might notice

It doesn't happen at exactly four months for everyone — timing varies from baby to baby. Common signs include more frequent night waking, shorter or harder-to-settle naps, more fussiness or clinginess around sleep, and sometimes changes in appetite. If your baby is otherwise happy, feeding and growing well, these are usually just part of the phase.

How long it lasts

The reassuring part: most sleep regressions pass within a couple of weeks as your baby adjusts to their new sleep pattern. Cleveland Clinic also notes that how parents respond can influence how long it lasts — calm, consistent responses tend to help it settle, while big changes to sleep habits can prolong it.

What gently helps

Keep a consistent, calming bedtime routine. The same soothing steps in the same order each night signal that sleep is coming.
Watch for overtiredness. An overtired baby is harder to settle. The Sleep Foundation notes a typical bedtime for a 4-month-old falls roughly between 6:30 and 8:00 pm, and that a slightly earlier bedtime can help prevent over-tiredness and support longer night sleep.
Lean on daylight and daytime activity. Bright, sociable days and dark, calm nights help the developing body clock tell day from night.
Offer a chance to self-settle. Putting your baby down drowsy but awake gives them the opportunity to practise falling asleep on their own, which can ease resettling between cycles.
Stay steady. Reassurance and consistency matter more than any single technique. Try not to introduce lots of new sleep crutches you'll want to undo later.
Keep safe sleep constant. Back to sleep, firm flat clear surface, every time — see our safe-sleep checklist.

What about the 8- and 12-month regressions?

You'll also see talk of regressions around 8 and 12 months. These are generally linked to other bursts of development — new motor skills like crawling and pulling to stand, and growing separation awareness — which can briefly disturb sleep. They're more variable and not every baby has them. The same fundamentals apply: a steady routine, age-appropriate timing, and calm, consistent responses.

When to talk to a doctor

Reach out to your pediatrician, GP or health visitor if the disruption lasts well beyond a couple of weeks, if your baby is feeding poorly or you're worried about their growth, or if anything simply doesn't seem right. Checking in is always reasonable — it can rule things out and set your mind at ease.

Back to the full guide

This is part of our baby sleep guide, which covers how much sleep babies need, safe sleep, bedtime routines and more.

Sources

Cleveland Clinic — The 4-month sleep regression: what parents need to know and Sleep in your baby's first year.
Sleep Foundation — 4-month sleep regression and infant sleep cycles.
Mayo Clinic — Helping baby sleep through the night.

Ninna is a monitoring app, not a medical device or healthcare provider. This article is general information, last reviewed June 2026, and is not medical advice. Always follow the guidance of your own doctor, pediatrician, GP or health visitor.