How long does the 4-month sleep regression last?

Usually two to six weeks. It is not really a step backwards — it is a permanent change in how your baby sleeps, so the goal is to adjust rather than wait for the 'old' sleep to return.

Is the 4-month regression a growth spurt?

They can overlap, but they are different. The regression is a change in sleep architecture — your baby now cycles through lighter and deeper sleep like an adult — while a growth spurt is a short burst of extra hunger.

Should I start sleep training at 4 months?

There is no need to rush. Many families simply adjust wake windows, tidy up the bedtime routine and wait it out. If you do choose a gentle settling approach, it is generally considered reasonable from around this age — but check with your pediatrician.

The 4-month sleep regression: why it happens and how to get through it

What the 4-month sleep regression really is, how long it lasts, and calm, practical things that actually help your baby (and you) sleep again.

Around four months, a baby who was sleeping beautifully can suddenly start waking every couple of hours, fighting naps, and needing far more help to settle. If that’s you right now: you’re not doing anything wrong, and your baby isn’t broken. This is the 4-month sleep regression, and it’s one of the most talked-about moments in a baby’s first year.

Why it happens

Here’s the reassuring part — it’s actually a sign of development. Around this age your baby’s sleep matures. Newborns drop straight into deep sleep; now your baby starts cycling through lighter and deeper stages, much like an adult. The catch is that between cycles there’s a brief surfacing to near-waking. Adults roll over and drift back. A four-month-old often fully wakes up — and then needs help to get back down.

Because it’s a permanent change in how sleep works, “regression” is a bit of a misnomer. Sleep isn’t going backwards; it’s growing up. That’s why the aim is to adjust, not to wait for the old sleep to come back.

How long it lasts

Typically two to six weeks. It passes faster when the days are set up to support the new kind of sleep — mostly through wake windows and a consistent wind-down.

What actually helps

None of this is a magic fix, but these are the calm, practical changes that make the biggest difference:

Watch wake windows. Overtiredness makes fragmented sleep worse. At this age most babies do well on windows of roughly 1.5–2.25 hours. See our wake windows by age guide.
A short, consistent bedtime routine. The same few calm steps in the same order — dim lights, feed, a book or a song — become a signal the body learns to trust.
Let them practice settling. When your baby stirs, pause a moment before rushing in. Sometimes they resettle on their own; every time they do, they’re learning.
Protect the first stretch. An age-appropriate, slightly earlier bedtime often gives you a longer first block of night sleep.
Full feeds during the day. At four months distractions are everywhere. Calm, complete daytime feeds mean less genuine hunger at night.

Be kind to yourself

This phase is exhausting precisely because it often follows a good stretch. Tag-team the nights with your partner if you can, lower the bar on everything else, and remember it’s temporary. It ends.

Take the guesswork out of the timing

The hardest part of this stretch is hitting the right nap and bedtime windows when everything has shifted. That’s what Nana is for — it learns your baby’s changing rhythm and tells you when the next sleep is due, so you’re not guessing on no sleep yourself.

Every baby is different, and this isn’t medical advice. If your baby seems unwell, isn’t feeding, or something worries you, contact your pediatrician.