The 4 Month Sleep Regression
What it is, why it happens, how long it lasts, and how to get through it
If your baby was sleeping reasonably well and suddenly everything feels off, you are not imagining it.
Around three to five months of age, many families experience what is commonly known as the 4 month sleep regression. Night waking increases, naps shorten, settling becomes harder, and sleep that once felt predictable can quickly feel exhausting and overwhelming.
This stage can feel confusing, especially when nothing obvious has changed. In reality, this regression is linked to a major and permanent shift in how your baby sleeps.
What is the 4 month sleep regression?
The term sleep regression is used to describe a temporary disruption in sleep, often linked to development or changing sleep needs. This can show up as more frequent night waking, short naps, increased fussiness, or needing more support to fall asleep.
At around four months, many babies begin to struggle with sleep even if they appeared to be good sleepers beforehand. This is not caused by habits, feeding choices, or routines you have created. It is driven by a biological change in sleep organisation.
If you are still in the early months, it can help to understand what is typical by revisiting what to expect with newborn sleep, as this stage marks the transition out of newborn sleep patterns.
Durign this period their sleep cycle architecture changes, they shift from 2 sleep stages(REM and N-REM) to four stages.
Is the 4 month sleep regression real?
Yes, and this is what makes it different from other regressions.
The 4 month sleep regression is the only regression directly linked to a biological change in sleep structure. Around this age, your baby’s brain matures and sleep begins to organise into defined sleep cycles.
To understand this shift, it helps to look more closely at newborn sleep cycles and how they differ from older baby sleep.
As these cycles mature, your baby begins moving through lighter stages of sleep more frequently overnight.
At the end of each sleep cycle, your baby briefly checks in with their environment. For some babies, this happens smoothly. For others, it becomes disruptive.
Why does this change cause more waking?
Around four months, your baby’s sleep becomes more structured and more “adult like”. Instead of drifting through newborn sleep, they start moving through clearer sleep stages in cycles, and they come into lighter sleep more often across the night.
Those moments of lighter sleep include tiny, normal arousals. Most adults roll over and keep sleeping. Babies often fully wake, because their brain is more alert now and their sleep is lighter at the end of each cycle. That is why you can suddenly see frequent waking, false starts, early mornings, or naps that start capping at one sleep cycle.
It is also a big stage of development. Increased awareness, new skills like rolling, changes in digestion, and a stronger need for connection can all make sleep feel more fragile. When you stack that on top of more frequent light sleep points, waking becomes much more likely.
If you are noticing repeated wake ups overnight, you may also want to explore why is my baby waking frequently, as multiple factors often overlap during this stage.
When does the 4 month sleep regression start?
For most babies, the 4 month sleep regression appears around four months of age.
However, it can begin as early as three months or closer to five months depending on individual development.
Why are naps suddenly so short?
Short naps are extremely common during the 4 month sleep regression and are usually linked to catnapping.
As sleep cycles mature, many babies start waking after a single sleep cycle during the day, often around 30 to 45 minutes. Day sleep is naturally less consolidated than night sleep, and the drive to stay asleep is lower, so it is much easier for them to fully wake at that transition and struggle to drift back off.
This can happen even when your routine is spot on, your baby settles easily, and the sleep environment is supportive. It is more about sleep development than anything you are doing wrong.
If your baby wakes happy, they have likely had enough rest to take the edge off.
How do awake windows impact the 4 month sleep regression?
As babies approach four months, awake windows need to gradually increase. Most babies at this age do best with awake windows between 90 and 120 minutes.
If awake windows are too short, sleep pressure may not be strong enough to support longer naps or stretches overnight. If they are too long, overtiredness can make settling and resettling harder.
A realistic 4 month sleep routine can help you assess whether your baby is under or overtired and guide small adjustments that support more settled sleep.
Why does feeding suddenly feel different?
Around four months, many babies become far more aware of the world.
Their vision improves, they notice movement and voices more easily, and they can get serious FOMO during feeds, popping on and off, turning their head, or getting distracted halfway through.
When daytime feeds become shorter or more broken, it is common for some of those calories to shift to overnight. At the same time, the four month sleep regression can bring more waking, and it is easy for feeds to start happening more often simply because everyone is awake more often.
If this pattern continues, some babies begin taking a large chunk of their intake overnight and eating less during the day. Over time, they can start waking genuinely hungry at night, which is known as reverse cycling.
So if feeds are suddenly harder in the day or nights are starting to feel increasingly feed heavy, it is worth looking at feeding patterns alongside sleep. Sometimes small changes like feeding in a quieter space, offering feeds more frequently during the day, or aiming for fuller feeds before naps can make a big difference.
Does the sleep environment matter at this age?
Yes, and it often matters more than people realise, because a lot of sleep environment changes tend to happen right around the same time as the 4 month regression.
Many babies begin rolling or showing signs of rolling at this age, which means it is time to stop swaddling for safety. Even if your baby was a great sleeper in a swaddle, that change in how their body feels, how their arms move, and how easily they can startle can temporarily disrupt both naps and nights. This does not mean anything is wrong, it is simply a big adjustment.
Some families also begin considering the move from bassinet to cot. This is often because baby is outgrowing the bassinet, waking from touching the sides, or moving more in their sleep. A cot can give them more space, but it is also a different sleep surface, a different room set up, and sometimes a different level of closeness to you, which can all take a little time to settle into.
When these environment changes overlap with the regression, they can add an extra layer of disruption. That is why it can feel like everything has shifted at once, even though each piece on its own is a normal developmental step.
The key is to keep the sleep space safe and consistent, make changes when you need to, and give your baby time to adjust while you support them through the transition.
Can you sleep train during the 4 month sleep regression?
Formal sleep training is generally not recommended until four months of age.
That said, understanding what sleep training actually is can help you feel more prepared and avoid jumping into changes too early. This stage is an ideal time to focus on routines, environment, and supportive settling rather than formal training.
As your baby approaches the next stage, a 5 month sleep routine often provides a clearer framework for more consolidated sleep which is when we personally recommend to start sleep training.
How long does the 4 month sleep regression last?
The neurological change that occurs around four months is permanent. Your baby does not return to newborn sleep once this transition has happened.
What we refer to as the “4 month sleep regression” is the adjustment period as your baby learns to move through these more mature sleep cycles. For most babies, this adjustment phase typically lasts around three to four weeks.
However, without changes to routines, awake windows, feeding patterns, and sleep support, the effects of the regression can continue well beyond this period. Frequent night waking, catnapping, and unsettled sleep are not signs that the regression is still happening, but rather that sleep needs have shifted and now require a different approach.
Once sleep is supported in line with this new neurological stage, many babies begin to show more settled nights and more predictable days again.
What helps the 4 month sleep regression pass more smoothly?
Supporting your baby through this stage does not require drastic changes. The goal is to strengthen the foundations so sleep has the best chance to settle as their sleep cycles mature.
Start with awake windows. Around this age, most babies do best with awake windows around 1.5 to 2 hours, and small tweaks of 10 to 15 minutes can make a noticeable difference. The right balance helps build enough sleep pressure for naps, reduces overtiredness, and can support longer stretches overnight.
Next, protect daytime feeds. Four month olds can get very distracted and feed in a stop start way, which can push more intake overnight. Feeding in a calmer space, offering feeds a little more frequently during the day, and aiming for fuller feeds before naps can help reduce the need to “catch up” at night.
Keep your night routine consistent and predictable. A simple wind down, the same steps in the same order, and a clear difference between day and night helps your baby understand what comes next. During regressions, consistency is more important than perfection.
Then focus on how your baby is supported to fall asleep and resettle. This is not about removing support overnight, it is about gradually helping your baby settle in their sleep space in a way that feels manageable for your family. If your baby wakes between cycles, using a consistent approach to respond can help those wakes stay shorter and calmer.
Creating a calm and predictable night routine and ensuring a sleep conducive environment can also support smoother transitions between sleep cycles.
This stage can feel intense, but it is temporary. With steady routines, realistic expectations, and the right support, most babies move through it with time.
What comes after the 4 month sleep regression?
As babies move beyond four months, sleep often begins to stabilise with the right support. Routines become clearer, naps start to lengthen, and night sleep becomes more predictable.
If you want structured guidance beyond this regression, the 5–24 Month Infant Sleep Course provides step by step support through routines, regressions, nap transitions, and developmental changes from five months onward.
For families wanting long term support that extends into toddlerhood, the Infant and Toddler Bundle offers guidance through sleep regressions, fears, separation anxiety, and big developmental leaps right through to four years.
Eva Beke
Certified Paediatric Sleep Consultant
Founder The Sleepy Little Bubs
I’m a certified paediatric sleep consultant and the founder of The Sleepy Little Bubs. I support families through baby and toddler sleep with practical, evidence-based guidance that considers the whole picture - sleep, development, routines, feeding, and family dynamics.
My approach is realistic, supportive, and designed to evolve as your child grows, so you’re not just getting help for today, but confidence moving forward.
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