The 4 Month Baby Sleep Regression: What It Is, Why It Happens, and How to Help Your Baby Through It

If you’ve noticed your once-sleepy baby suddenly waking up every hour, crying more during the night, and fighting naps like never before… you’re not alone. Welcome to what many parents know (and fear) as the 4 Month Sleep Regression.

The good news? It’s not really a regression at all. It’s actually a powerful progression—a developmental milestone that marks a major shift in your baby’s sleep cycles. And while it can be tough in the moment, understanding what’s happening behind the scenes can help you support your baby through it—and come out the other side with better sleep than ever.

So, What Is the 4 Month Sleep Regression?

Around 3 to 4 months of age, your baby’s sleep pattern undergoes a major transformation. Until now, your little one has only experienced two stages of sleep: deep (slow-wave) sleep and REM (rapid eye movement) sleep.

But around the four-month mark, your baby begins to adopt the adult-like 4-stage sleep cycle, which includes:

1. Stage 1 – Drowsy and drifting

2. Stage 2 – Light sleep

3. Stage 3 – Deep, restorative sleep

4. Stage 4 – REM sleep

   
   

This reorganization is permanent—your baby is essentially graduating to mature sleep! While this is a positive milestone, it comes with a catch: your baby is now spending more time in lighter sleep, which makes them more likely to wake up. And without the ability to fall back asleep independently, they often cry for help—again and again, throughout the night.

Why This Feels So Disruptive (for Everyone)

As adults, we wake up during the night too. But we’re able to recognize our surroundings, understand it’s safe, and fall back asleep—often without even remembering we woke up at all. A four-month-old, however, lacks this reasoning. If your baby fell asleep nursing, being rocked, or with a pacifier, they wake up expecting those same conditions. When they find themselves alone in a quiet crib, confusion and fear can set in, triggering full-blown wakefulness. That’s when the cycle begins—frequent night wakings, fussiness, short naps, and very tired parents.

The Silver Lining: This Is a One-Time Shift

While the four-month sleep regression can be intense, it’s also a one-time developmental change. Once your baby adjusts, they’ll follow this sleep cycle for the rest of their life. So rather than fighting it, this is the perfect time to help your baby develop independent sleep skills that will serve them for years to come.

How to Help Your Baby Through the 4 Month Sleep Regression

Here are my top strategies as a professional sleep consultant to help you and your baby navigate this transition with confidence.

1. Make the Room Pitch Black

Light exposure is a major sleep disruptor. Even small amounts of light—streetlights, nightlights, hallway glow—can signal the brain that it’s time to be alert. So aim for coal mine on a moonless night darkness. Use blackout curtains, tape garbage bags to the windows, or cover them with foil if needed. (Just don’t be surprised if your neighbors get curious.) Infants aren’t afraid of the dark—but they are sensitive to light. Darkness helps signal melatonin production and promotes deeper sleep.

2. Add White Noise

Now that your baby is in lighter sleep more often, everyday noises—dogs barking, delivery trucks, siblings playing—can easily wake them. A white noise machine creates a consistent, soothing background sound that masks household noise and supports longer, uninterrupted sleep. It’s a “sleep prop,” yes, but one that doesn’t require parental presence or intervention—so it’s a keeper.

3. Stick to a Consistent Bedtime Routine

Babies thrive on predictability. A short, calming bedtime routine helps cue your baby that sleep is coming. Aim for 4 to 5 simple steps: bath, feed, story, lullaby, and into the crib awake.

Pro tip: Don’t let feeding be the final step. If your baby nods off at the breast or bottle, they may develop a sleep association that becomes a challenge during night wakings. Move the feed earlier in the routine, followed by less stimulating activities that gently lead toward sleep.

4. Watch the Clock

At four months, babies can usually stay awake for about 2 hours at a time. Pushing past that window often leads to overtiredness, which makes falling asleep (and staying asleep) much harder. Also, aim for a bedtime between 7:00 and 8:00 PM, when your baby’s natural melatonin production kicks in.

When to Get Help

Some babies sail through this milestone with minimal trouble. Others struggle. If you're finding yourself exhausted, overwhelmed, or unsure what to do next—you don’t have to go it alone.

I offer a free 20-minute sleep evaluation so I can learn more about your baby’s unique situation and offer personalized guidance. Whether you need a complete sleep plan or just a few tweaks, I’m here to help you and your baby sleep better—sooner. Most parents tell me, “I wish I’d reached out sooner!” So if you're on the fence, take that first step. You’ll be so glad you did.

👉 Let's book your free call today and let’s move forward—together—toward peaceful nights and well-rested mornings.