Why Sleep Changes At 4 Months

Understanding the 4 Month Sleep Regression

Just when you feel like you’re starting to get into a nice rhythm with sleep, your baby reaches around four months and everything seems to change. Suddenly, they’re waking more often overnight, naps might become shorter or harder to settle, and you’re left wondering what on earth has happened.

First, let me reassure you. This is a very common and very normal stage.

Around four months, your baby goes through the biggest biological shift in their sleep development. Until now, their sleep has been quite immature and they’ve often drifted between sleep cycles without fully waking. From this point on, their sleep starts to look more like adult sleep, with clearer, more defined cycles.

What that means in real life is that instead of briefly stirring between cycles, your baby now wakes fully. They become more aware of their surroundings, and if they don’t yet have the skills to settle themselves back to sleep, they’ll need your help to get there.

This is why so many parents notice a sudden increase in night waking around this age.

Demystifying the 4 Month Sleep Regression

So why does your baby seem to struggle to go back to sleep when they used to manage just fine?

The key thing to understand is sleep associations. The way your baby falls asleep at the start of a nap or at bedtime is what they learn to rely on to fall asleep again. If they’re fed, rocked, or cuddled all the way to sleep, that becomes the “recipe” their brain expects when they wake between cycles.

When your baby naturally wakes at the end of a sleep cycle and that same situation isn’t there, they don’t yet know how to get back to sleep without it.

Imagine it from their point of view. You drift off to sleep in someone’s arms, warm, cosy, and feeling safe. You can smell them, hear them, and feel their presence. Then you wake up and you’re in a dark room, in a cot, and everything feels different. Of course you’d feel unsettled. Of course you’d call out.

That’s not your baby being difficult. That’s your baby being completely normal.

So What Can Help?

One of the most helpful changes you can make at this stage is to start putting your baby into their cot before they’re fully asleep.

This doesn’t mean you can’t still have a cuddle, a feed, or a gentle rock. Those things are lovely and comforting. The aim is simply to let your baby go into their cot while they’re still awake enough to do the final part of falling asleep themselves.

When babies learn to fall asleep in their own sleep space, they’re much more likely to be able to resettle there when they wake between cycles overnight. The environment feels the same, and their brain recognises it as a safe place to drift back off.

This skill, often called self-settling, isn’t about leaving your baby to cry or cope alone. It’s about gently giving them the opportunity to practise falling asleep in a way that they can repeat during the night.

Looking Ahead

The four month sleep regression can feel exhausting, especially if sleep had been going reasonably well before. But it’s also a sign that your baby’s sleep is maturing and developing, which is a good thing in the long run.

With the right support, consistent routines, and gentle changes to how your baby falls asleep, most families come through this stage with stronger sleep foundations in place.

If you’re in the thick of it right now, be kind to yourself. You’re not doing anything wrong. Your baby’s sleep has simply changed, and sometimes a few small, supportive tweaks are all that’s needed to help everyone get back to more settled nights again.