What to Expect During the 4-Month Sleep Regression

Just when you thought your baby was finally sleeping longer stretches at night, everything unravels. They’re waking up every two hours again. Naps are shorter, fussiness is up — and so is your exhaustion. If this sounds familiar, you might be smack in the middle of the 4-month sleep regression.

This stage can feel like a rude surprise, especially if your baby was just beginning to develop a predictable routine. But it’s actually a normal — and important — milestone in your baby’s development.

In this article, we’ll break down exactly what the 4-month sleep regression is, why it happens, how long it lasts, and — most importantly — what you can do to support your baby (and yourself) through it. By the end, you’ll feel less overwhelmed and more empowered with the right information and tools.

What Is the 4-Month Sleep Regression?

A Developmental Milestone, Not a Setback

Contrary to how it feels, the 4-month sleep regression isn’t a sign that something’s gone wrong. In fact, it’s a sign that your baby’s brain is growing and maturing.

At around 3 to 5 months, babies transition from newborn-style sleep (mostly light sleep with little pattern) to more mature sleep cycles that resemble those of adults. This means they start experiencing light, deep, and REM sleep — and they begin to wake more frequently between cycles.

Why It Feels So Sudden

What makes this regression so tricky is how abruptly it can appear. One day your baby may be sleeping six hours straight, and the next, they’re up every hour. This shift often catches parents off guard.

Common Signs Your Baby Is Going Through It

Recognising the symptoms can help you respond with more empathy and less frustration.

Here’s what to look out for:

• Frequent night wakings (every 1–2 hours)
• Shorter naps — 20 to 45 minutes instead of full sleep cycles
• Increased fussiness or crankiness during the day
• Changes in feeding habits — more distracted or hungrier than usual
• Difficulty falling back asleep independently

If your baby is around 4 months old and suddenly struggling with sleep, it’s likely this regression at play.

What Causes Sleep Regressions in Babies?

Brain and Body Are Rapidly Developing

At 4 months, babies are undergoing a flurry of neurological and physical growth:

• Improved vision and sensory awareness
• More intentional movement and rolling over
• Social awareness, like recognising familiar faces
• A stronger circadian rhythm

These exciting changes mean their brains are more stimulated — and, unfortunately, less likely to switch off at bedtime.

Sleep Cycle Maturation

Babies now experience more defined stages of sleep. But they haven’t yet developed the self-soothing skills needed to transition smoothly from one cycle to the next. So they wake up fully — and need help getting back to sleep.

How Long Does the 4-Month Sleep Regression Last?

This varies from baby to baby, but the regression typically lasts 2 to 6 weeks.

Factors that affect the duration include:

• Your baby’s temperament
• Their ability to self-settle
• The sleep environment
• Your consistency with routines

While it may feel endless, this phase is temporary, and there are steps you can take to make it more manageable.

Coping Strategies That Actually Work

1. Stick to a Consistent Sleep Routine

Now more than ever, your baby needs predictability.

Establish a soothing bedtime routine that signals sleep is coming, such as:

• Bath
• Feeding
• Story or lullaby
• Cuddles
• Lights out

Keep this routine short and calming, lasting no more than 20–30 minutes.

2. Optimise the Sleep Environment

Small tweaks can make a big difference in your baby’s sleep quality.

Try to ensure:

• The room is dark (use blackout blinds)
• A white noise machine runs during naps and bedtime
• The room is at a comfortable temperature (18–20°C)
• There are no harsh lights or overstimulating toys in the crib

Creating a conducive sleep setting helps your baby transition between cycles with less disruption.

3. Practice Safe Sleep Habits

Follow the safe sleep guidelines recommended by the NHS:

• Place baby on their back to sleep
• Keep the crib free of pillows, toys, and loose bedding
• Share a room, not a bed, for the first 6 months

These habits not only protect your baby but promote more restful, uninterrupted sleep.

4. Support (But Don’t Rescue) Every Wake-Up

During the regression, your instinct may be to feed or rock your baby back to sleep immediately. While comforting is essential, it’s also helpful to give them a few minutes to try resettling on their own.

Gradually, they’ll begin to link sleep cycles without full parental intervention.

For help navigating sleep regressions that follow, our post on what to expect during the 4-month sleep regression can guide you through that next phase with clarity and calm.

Should You Sleep Train During the 4-Month Regression?

It Depends on Your Baby (And You)

Many experts suggest holding off on formal sleep training during the height of this regression. Since your baby is adjusting to a whole new sleep architecture, trying to enforce a rigid routine can backfire.

Instead, focus on:

• Establishing a strong sleep foundation
• Introducing sleep cues and calming techniques
• Watching for tired signs (rubbing eyes, yawning, zoning out)

If you choose to begin sleep training, wait until the regression has passed and your baby is at least 5–6 months old.

Take Care of Yourself, Too

Sleep Deprivation Isn’t Just a Baby Problem

Parents often describe this phase as “relentless”, and that’s no exaggeration. Lack of sleep affects everything — mood, mental clarity, physical health, and relationships.

Support strategies for you:

• Nap when the baby naps — even 20 minutes helps
• Share nighttime duties with a partner, friend, or family member
• Keep easy snacks and water by your bed
• Don’t hesitate to ask for help — you’re not supposed to do this alone

You might also explore our mindful eating routines to help stay grounded, nourished, and resilient during these changes.

The Long-Term Sleep Outlook

It Gets Better — Really

Once your baby’s sleep cycles stabilise and they learn to self-soothe, longer stretches return. In fact, this regression lays the groundwork for more mature sleep patterns in the months to come.

It’s a hard season, but it’s also a passing one — and often the first big challenge in your baby’s evolving sleep journey.

Your Baby’s Brain Is Growing — And So Are You

The 4-month sleep regression can be brutal, but it’s also a reminder of how quickly your baby is growing and changing. Each tough night is a step closer to more stable, restful routines.

By understanding the causes and applying calming, consistent strategies, you’re helping your baby adapt — and giving yourself the tools to cope along the way.

You don’t need to be perfect. You just need to be present, flexible, and kind to yourself.

Breathe. This too shall pass — and your sleep (eventually) will return.