4 month sleep regression - signs, causes and tips

What is a 4-month sleep regression?

Around 3-4 months of age, it’s common for a baby’s sleep to suddenly take a turn for the worse, even if things were going smoothly before. Your baby might start waking up more frequently at night, be harder to put down for bedtime, or take shorter naps during the day despite being tired. This is often called a sleep regression.

The cause is believed to be a developmental leap that changes your baby’s sleep cycles.

While "sleep regression" isn’t a term used in medical care, it’s a name that parents and some authors have coined to describe these changes in a child’s sleep.

Signs of a 4-month sleep regression

• More frequent night wakings

• Fussiness

• The baby only wants to sleep on or close to a parent, even if they previously could be put down easily

• Short naps despite being tired

• Challenging bedtimes that take a long time

• Other changes in sleep that don’t seem to have a clear cause

Why does a sleep regression happen at 4 months?

As children develop physically and mentally, changes in sleep are common. Many parents notice a significant shift around four months, and this sleep regression is often the most noticeable—making it the most well-known.

This particular sleep regression can feel especially pronounced because, at this age, your baby undergoes a major change in their biological sleep pattern. Around 3-5 months, your baby transitions from a newborn sleep pattern to having sleep cycles with different stages of sleep depth, similar to those of an adult. During this time, your baby’s sleep needs also change, and they become more aware of their surroundings while practicing new skills.

The shift in sleep cycles explained

A newborn spends about half of their sleep in what's called active sleep. During this time, your baby can be easily woken up—whether it's because they're disturbed, hungry, or simply because they've had enough sleep.

Around 9-15 weeks, your baby starts developing their circadian rhythm and begins producing melatonin in response to light, darkness, and routines. As sleep matures, your baby's sleep pattern shifts, and they start sleeping more like an adult, with four sleep stages instead of just two.

Reversed cycling

If your baby is waking up more frequently at night and you're used to nursing or bottle-feeding to help them fall back asleep, it’s not uncommon for them to fall into what's called reverse cycling. This means your baby starts feeding more often in response to those increased night wakings around 3-4 months old. At the same time, your baby is becoming more curious about their surroundings and can easily get distracted during daytime feedings. The combination of these factors can shift your baby’s energy intake more toward the night, making it harder for them to learn to fall back asleep since they actually start feeling hungry during those frequent night wakings.

Increased awareness of surroundings

At this age, your baby becomes more aware of their surroundings. You might start noticing that they show stronger emotions about being separated from you—like only wanting to sleep on or near you. Your baby may also react more to differences in their environment between falling asleep and waking up. For example, they might fall asleep while being rocked in your arms but then wake up alone in their crib. During this period, many parents find it helpful to get their baby used to falling asleep in the same place where they'll later sleep and wake up.

Changed sleep needs

Around this time, your baby’s wake window usually increases to about 90-120 minutes. If they’re on the lower end of this range, it can sometimes affect how tired they feel at bedtime and how strong their sleep pressure is at night—making it easier for them to wake fully at the end of each sleep cycle.

If your baby consistently has shorter wake windows throughout the day, you might consider gradually stretching those wake windows a bit. Start slowly and give your baby a few days to adjust so they don’t become overtired.

Motor and mental development

Around 4 months, your baby is also busy practicing new skills. They’re working on hand-eye coordination and trying to learn how to roll over. They might also be exploring their voice, making different sounds, and starting to babble. While this development might not be as pronounced as in later stages, your baby is still so young that they can easily become overstimulated by all these new things, which can affect their sleep.

When does the 4-month sleep regression start? Can it start early?

The most common time for the sleep regression is around 4 months. However, some babies may show signs as early as 3 months or a little later, closer to 5 months. If your baby was born prematurely, the timing might also shift and occur closer to their adjusted age.

How long does the 4-month sleep regression last?

The sleep regression usually lasts about 2-6 weeks. However, the effects can last much longer if your baby falls into a reverse cycling pattern or if it’s difficult to help them learn to self-soothe during night wakings. Night wakings can also persist if you don’t find a good rhythm with wake windows and naps, leaving your baby not tired enough at night.

How to handle the 4-month sleep regression

The 4-month sleep regression is usually most noticeable for a few weeks, but its impact on routines can last much longer. How you handle the changes during this time can make a big difference. Understanding your baby’s needs during this phase can be key to coming out of it with better sleep patterns, rather than worse.