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Is your 4-month-old suddenly waking up every hour, fighting naps, or struggling to sleep at night? You’re not alone. The 4-month sleep regression is a common milestone in infant sleep development. But don’t worry—this phase is temporary, and there are ways to help your baby (and yourself) get better rest.

What is the 3- to 4-month sleep regression?

There’s a point in every parent’s journey when your little baby starts to sleep better...and you’re so relieved and so happy. But then…a bump in the road! Seemingly overnight your 3- or 4-month-old baby’s sleep patterns change for the worse. Why? When babies reach between 3 and 4 months old, their sleep cycles shift and their development is simply blooming, which can temporarily hinder sleep.

Signs Your Baby Is Going Through the 3- to 4-Month Sleep Regression:

If your little one used to be a stellar sleeper and now—suddenly—they are not, sleep regression might be to blame. Sleep regression signs include:

Why is my 4-month-old not sleeping?

At 4 months your baby is emerging from the fourth trimester…and their brains and bodies are rapidly changing! For one, up until this point, they had two distinct stages of sleep: rapid eye movement (REM) sleep and non-rapid eye movement (NREM), spending about equal time in both. Once they hit the 3- to 4-month mark, they go through four stages of sleep. They’re also waking up to the wider world! Your little one is transforming into quite the social creature. So now they fall into light sleep and wake up craving stimulation! 

A few reasons why your 4-month-old isn’t sleeping include:

  • Their sleep cycles are shifting.

  • They’re more aware and interested in the world around them.

  • They’re going through developmental changes.

  • They’re growing and might be waking up hungry.

Why do babies experience the 3- to 4-month sleep regression?

What’s changed? Your little blob of a newborn is now a 3- or 4-month-old social butterfly. They fall into a light sleep and wake up…bored! It’s too quiet and too still for your sweet pea. Your company-loving 4-month-old will wake up and think, “Hey you! Come back! I want to play!” But your baby’s new-found social tendencies aren’t the only thing contributing to the 3- to 4-month sleep regression. Your baby may also be…

  • Learning to roll over. When that happens, you have to stop swaddling, which may mean your baby cries and wakes more often. (Of note: If your baby is sleeping in SNOO, they can remain safely swaddled until they graduate to the crib.)

  • Experiencing a growth spurt. And man, will they be hungry!

  • Teething or dealing with a cold. These types of mild discomforts can easily disrupt a baby’s sleep.

  • More sensitive to temperature or light. As babies become more aware of the big world around them, new sensitivities can arise.

Why is the 4-month sleep regression so hard?

The 4-month sleep regression hits many parents like a ton of bricks—and for good reason! This particular sleep bump comes at a time when you may have just started to feel like you and your baby were getting into a groove. Then suddenly…bam! Naps shorten, nights stretch into endless wake-ups, and everyone’s cranky.

What makes this sleep regression especially tough is that it’s not just about a growth spurt or a temporary blip. Around this age, your baby’s sleep matures in a big way. Instead of drifting between deep and light sleep in long stretches like a newborn, your baby starts cycling through more adult-like sleep stages. That means more frequent wake-ups—especially during the lighter stages of sleep—and your little one might need help learning how to fall back asleep on their own.

On top of that, your baby is becoming more aware of the world. New sounds, sights, and sensations can all be wonderfully exciting…which also means they can be distracting when it’s time to sleep.

Yes, the 4-month sleep regression can be rough—but it’s also a sign that your baby is growing and developing just as they should. With patience, consistency, and a few smart sleep strategies, you’ll both make it through to brighter (and more restful) days ahead.

Signs Your Baby Is in the 4-Month Sleep Regression

Wondering if your baby has hit the 4-month sleep regression? Here are some common signs to look out for:

  • Sudden night wakings (especially after a stretch of longer sleep)

  • Shorter naps or more unpredictable daytime sleep

  • Trouble falling asleep at bedtime

  • Fussiness or crankiness during the day from poor sleep

  • Increased sleepiness, but difficulty staying asleep

  • More frequent night feedings (even if your baby had been going longer between feeds)

  • Needing more help to fall back asleep, like rocking, feeding, or being held

  • Increased alertness or distractibility, even when tired

If several of these signs are popping up, your baby is likely going through this normal developmental stage. With some extra support and consistent routines, more restful nights are ahead!

How long does the 4-month sleep regression last?

Like so many things in babyhood, the answer is: It depends. For some families, the 4-month sleep regression lasts just a few days. For others, it can stretch on for several weeks—or even longer—especially if healthy sleep habits haven’t been established yet.

The silver lining? You’re not powerless here. Creating a consistent bedtime routine, making sure your baby gets enough daytime sleep, and introducing gentle sleep strategies (like the wake-and-sleep method) can help ease your baby through this tricky phase. The more your little one learns to self-soothe and connect their sleep cycles, the quicker this regression tends to pass.

Remember, this phase is temporary. With time—and a little help from you—your baby’s sleep will settle into a more predictable rhythm.

How to Handle the 3- to 4-Month Sleep Regression:

Most parents are blindsided by the 3- to 4-month sleep regression and don’t know what to do. But if you learn to establish healthy sleep habits, you may be able to steer clear of most, if not all, of it. Here are more time-tested strategies for helping to avoid—and cope with—the 3- to 4-month sleep regression:

  • Continue to swaddle if you can. Swaddling babies safely helps bring on the ZZZs. Being swaddled is a similar experience to being carried in a sling, cuddled skin to skin, and being in the womb. The soft, snug caress of a swaddle can soothe babies for hours! (If your baby is rolling, swaddling needs to stop unless your baby is sleeping in SNOO. In that case, they can remain safely swaddled up to 6 months while in the bassinet.)

  • Tune into Baby’s wake windows. Having a sense of how long your baby can (and should) be comfortably awake between sleeps is key to having a well-rested and happy baby. Learn how to recognize your baby’s sleepytime cues and how to pinpoint their wake windows with our wake windows guide.

  • Turn on white noise. Although your baby’s natural calming reflex begins to fade around 3 to 4 months old, white noise continues to help with sleep. While white noise used to flip on baby’s inborn “on switch” for sleep, now the sleepy reaction comes from habit. Once you start using white noise in the background of baby’s bedtime routine, they’ll start to expect it and make the connection that white noise means sleepytime is here.

  • Try using sound with rocking. Using the right types of motion and sound can help your baby gently slide into the light sleep part of their sleep cycle without being easily roused. Since baby’s should never sleep in a baby swing, the only safe alternative is rocking your baby all night long in your arms (not feasible!) or using SNOO. SNOO ensures babies can rock all night while securing them on their backs. (Learn all about how rocking bassinets help babies sleep.)

  • Encourage more daytime eating. You can start to anticipate (and decrease) nighttime hunger by encouraging your baby to eat a little more during daytime feeds. It also may be smart to introduce a dream feed between 10pm and midnight. (This is when you rouse your baby without fully waking them to feed one more time before you go to bed. Sneaking in an extra feed has been shown to reduce night wakings.)

  • Get outside. Fit in plenty of outdoor time, complete with fresh air and (safe!) sunlight exposure will help your little one recognize the difference between day and night. Morning light especially helps your baby’s brain release melatonin, a hormone that regulates sleep and wakefulness, at the right time for night-night.

  • Keep Baby’s room dark. A dark room does a great job at encouraging sleep. Plus, if your baby wakes too soon, the darkness works to help you baby fall back asleep.

  • Help your baby self-soothe. If you haven’t already, I suggest introducing your baby to my wake-and-sleep trick. Every bedtime, swaddle your baby, turn on the white noise, feed and burp them, and if your baby falls asleep in your arms before you lay them down in their bassinet, gently rouse them with a light tickle on their feet until they barely wake. After a few seconds, they’ll close their eyes and slide back to sleep. (If your baby fusses, pick them up for a feed or a cuddle, then repeat the tickle-to-wake routine.) Those few seconds of drowsy wake-time are the first steps to helping your baby learn how to self-soothe and sleep longer.

How to Survive the 4-Month Sleep Regression

The 4-month sleep regression can feel exhausting, but there are ways to manage it. Here’s how you can survive this challenging sleep phase and help your baby adjust to new sleep patterns:

  • Follow a calming bedtime routine (e.g., warm bath, white noise, dim lights).

  • Make sure your baby is getting enough daytime sleep—overtiredness can make sleep issues worse!

  • Try gentle sleep training techniques suited for 4-month-olds, like the Wake and Sleep method–which helps babies learn to fall asleep on their own without needing to “cry it out”.

How SNOO Can Help Prevent The 3- to 4-Month Sleep Regression

Happiest Baby’s SNOO Smart Sleeper is a big help and parents’ best tool for preventing the 3- to 4-month sleep regression. SNOO teaches babies to be better sleepers by improving their day/night sleep pattern from day one and by using the rhythms they’re naturally familiar from the womb. (SNOO’s rocking, white noise, and swaddling are all part of the 5 S’s for soothing babies.) At the same time, SNOO quickly responds to your baby’s fussing before they fully wake up, which greatly contributes to everyone sleeping better. And because of SNOO’s patented swaddling system that keeps babies on their backs, SNOO babies can remain swaddled longer worry-free. (Traditional swaddling must stop when Baby can roll.)

SNOO is so effective, in fact, that SNOO babies can often sidestep the dreaded 3- to 4-month sleep regression entirely! But even if your baby does go through the 3- to 4-month sleep regression in SNOO, those with a Premium App subscription can easily adjust SNOO’s settings and “lock” SNOO at a higher level to promote sleep all night long.  Just like you would rock and hold your baby more vigorously when they’re going through a hard time, leveling SNOO up similarly “ups the ante.” Because you can so easily customize SNOO, I like to think of it as a “spot cure” during any stint of wakefulness (a growth spurt, a cold), giving babies the extra soothing they need so that when they stir, they don’t wake up all the way.

For more help getting your baby to go to sleep—and stay asleep— check out:

About Dr. Harvey Karp

Dr. Harvey Karp, one of America’s most trusted pediatricians, is the founder of Happiest Baby and the inventor of the groundbreaking SNOO Smart Sleeper. After years of treating patients in Los Angeles, Dr. Karp vaulted to global prominence with the release of the bestselling Happiest Baby on the Block and Happiest Toddler on the Block. His celebrated books and videos have since become standard pediatric practice, translated into more than 20 languages and have helped millions of parents. Dr. Karp’s landmark methods, including the 5 S’s for soothing babies, guide parents to understand and nurture their children and relieve stressful issues, like new-parent exhaustion, infant crying, and toddler tantrums.

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Disclaimer: The information on our site is NOT medical advice for any specific person or condition. It is only meant as general information. If you have any medical questions and concerns about your child or yourself, please contact your health provider.