The four month sleep regression typically lasts 2 to 6 weeks, though some babies adjust in as little as one week while others take closer to eight. Unlike later sleep regressions, this one marks a permanent change in how your baby sleeps, which is why it can feel more disruptive and less predictable than a simple rough patch.
Why This Regression Is Different
Around four months, your baby’s brain reorganizes the way it handles sleep. Newborns cycle between only two states: active sleep (similar to REM) and quiet sleep (similar to deep sleep), with each cycle lasting about 45 to 60 minutes. At four months, the brain starts transitioning to a more adult-like pattern with distinct stages of light sleep, deep sleep, and dreaming.
This matters because between each new sleep cycle, your baby now passes through a brief period of very light sleep. Adults do this too, but we’ve learned to roll over and drift off again without noticing. Your baby hasn’t. So every 45 to 60 minutes, they may partially wake up and need help getting back to sleep. The regression isn’t really a regression at all. It’s a one-way upgrade to a more complex sleep system, and the disruption you’re seeing is your baby learning to navigate it.
What It Looks Like
The hallmark signs are increased night wakings, shorter naps, and more difficulty falling asleep at bedtime. A baby who had been sleeping in longer stretches may suddenly wake every one to two hours. Naps that used to last over an hour might shrink to 30 or 40 minutes, because your baby wakes at the end of one sleep cycle and can’t bridge into the next.
You’ll also likely notice more fussiness during the day. Around this age, babies are hitting a wave of developmental milestones: holding their head steady without support, pushing up on their forearms during tummy time, swiping at toys, and bringing hands to their mouth. They’re also becoming more socially aware, smiling to get your attention and making cooing sounds. All of this new brain activity can make it harder to wind down. Some babies seem to want to “practice” their new skills in the crib rather than sleep.
Growth Spurt or Sleep Regression?
These two often overlap at four months, which makes things confusing. The key difference is duration and symptoms. A growth spurt typically lasts only a few days and comes with a noticeable spike in hunger. You’ll see more frequent hunger cues like rooting, tongue thrusting, hand sucking, and general restlessness around feeding times. Once the spurt passes, sleep usually bounces back.
A sleep regression, by contrast, centers on sleep itself: more night wakings, shorter naps, and trouble settling. Your baby’s appetite may increase somewhat, but the core problem is that they keep waking up and can’t get back to sleep on their own. If the disruption stretches past a week and hunger doesn’t seem to be the main driver, you’re most likely dealing with the regression.
What Helps During Those Weeks
You can’t speed up the neurological changes happening in your baby’s brain, but you can make the transition smoother. The most effective strategies focus on teaching your baby the difference between day and night and giving them small opportunities to practice settling on their own.
During nighttime wakings, keep the room dark or dimly lit and your interactions quiet and brief. Feed in the bedroom if possible, and save play and stimulation for daytime. This contrast helps reinforce your baby’s developing circadian rhythm, which is still maturing at this age.
Try putting your baby down drowsy but awake. This doesn’t mean leaving them to cry. It means placing them in their crib when they’re sleepy and giving them a minute or two to settle before stepping in. If they grizzle, that brief pause lets them attempt to self-soothe. If grizzling escalates to actual crying, comfort them and help them settle. The goal is small, low-pressure practice, not a test of endurance.
A consistent pre-sleep routine also makes a difference. It doesn’t need to be elaborate. A simple feed-play-sleep pattern during the day, and a predictable sequence of events before bedtime (dim lights, feed, a few minutes of quiet holding, then into the crib) gives your baby cues that sleep is coming. Predictability is genuinely calming for a brain that’s processing a lot of new information.
When Sleep Training Fits In
Four months is the earliest age most experts consider appropriate for formal sleep training, because babies haven’t developed the circadian rhythms needed to sleep through the night before then. That said, six months is generally considered a better starting point. If your baby begins falling asleep on their own at bedtime, even if they still wake during the night, that’s a sign they may be ready.
Most babies sleep through the night somewhere between 4 and 9 months old, so there’s a wide range of normal. If you’re in the thick of the four month regression, it’s reasonable to focus on gentle settling strategies first and revisit sleep training once the worst of the disruption has passed. Trying to sleep train during the peak of the regression can be frustrating for everyone, because your baby is adjusting to a fundamentally new sleep architecture and may not yet have the neurological readiness to respond well.
How You’ll Know It’s Over
The regression doesn’t end with a sudden return to how things were before. Because your baby’s sleep structure has permanently changed, “over” looks different than it did with earlier rough patches. What you’ll notice is a gradual improvement: night wakings become less frequent, naps start stretching past a single sleep cycle again, and bedtime becomes less of a battle. For most families, this shift becomes noticeable somewhere between 2 and 6 weeks after the disruption started.
Some babies settle into their new sleep pattern quickly and seem to resolve in a couple of weeks. Others, especially those who relied heavily on being rocked or fed to sleep, may take longer because they need more time to learn how to reconnect sleep cycles independently. Neither timeline means anything is wrong. The underlying change is the same; the adjustment period just varies.