The Four Month Sleep Regression Explained

November 19, 2021

Four Month Sleep Regression Explained- updated 8/16/2025

The 4-Month Sleep Regression Explained in 30 Seconds

Newborns only go through 2 stages of sleep, but at 4 months old begin maturing into the 4 stages of sleep that we keep for the rest of our lives. The two new stages include lighter sleep. The 2 new stages mean more frequent night wakings and shorter naps. This is because for the first time in baby’s whole life, it’s easier for them to get woken up and they don’t yet know how to get themselves back to sleep.

It’s a normal progression that happens before your baby is able to sleep longer stretches overnight. It can be frustrating but knowing why and when it’s happening, and being prepared to ease the transition can help. Sticking to consistent routines, using soothing techniques like a pacifier and trying to let your baby fall asleep independently can all help with the transition to more mature sleep.

The 4 Stages of the Sleep Cycle

In order to understand how your full-term baby is developing with regard to sleep around four month’s old, we first need talk about sleep in general.

Many of us just think of sleep as an on-or-off situation. You’re either asleep or you’re not. But sleep actually has a number of different stages that make up the “sleep cycle.” Starting at 4 months old, the brain matures into going through all 4 of the stages several times a night and this is the cycle we use for the rest of our lives.

• Stage 1 is that initial stage we’re all familiar with where you can just feel yourself drifting off, but don’t really feel like you’ve fallen asleep. In this stage, you could still hear your name if someone called you and it’s very easy to wake up.

• Stage 2, considered the first “true sleep” stage. This is where people tend to realize, once woken up, that they actually were sleeping.

• Stage 3 is deep and regenerative. Also known as “slow wave” sleep, this is where the body starts repairing and rejuvenating the immune system, muscles tissue, energy stores, and sparks growth and development.

• Stage 4 is REM (rapid eye movement) sleep. This is where the brain starts to kick in and consolidates information and memories from the day before. It’s also the stage where we do most of our dreaming.

Once we’ve gone through all of the stages, we either wake up, or come close to waking up, and then start over again until morning.

Sleep from Newborn to 4 Month’s Old

Newborn babies only have 2 stages of sleep; stage 3 and REM. They spend about half their sleep in each stage. At around the third or fourth month, there’s a reorganization of sleep, as they embrace the 4-stage method of sleep described above.

When the change to the 4 stage method of sleep takes place, baby moves from 50% REM sleep to 25%, in order to make room for those first two stages. Although REM sleep is light, it’s not as light as the 2 new stages of sleep they’re getting used to. With more time spent in lighter sleep, there’s more of a chance that baby will wake up.

Waking up is absolutely natural, and we continue to wake up three, four, five times a night into adulthood. As adults however, we’re able to recognize that we’re in bed and safe and we go back to sleep. This usually happens so quickly that we don’t even remember in the morning.

For a four-month old infant though, these types of wake-ups are something they’ve never experienced before in their whole life! So it makes sense that they need our help to get back to sleep. Whether they’re usually rocked back to sleep, need a pacifier or just need reassurance, your baby most likely will not go back to sleep without your help.

How to Get through the Four Month Sleep Regression

Unless you have a unicorn baby who does not need your help to go to sleep, the other contributor to infant’s waking up more often overnight is that their “normal” is facilitating sleep with a pacifier, by being rocked or by being breastfed. Let me say this part in all caps though: getting baby to sleep these ways are ALL NECESSARY, NORMAL AND NOT “BAD HABITS.”

To get through the 4 month sleep regression, or any sleep disturbances you can:

• Use a pacifier – At 4 months, more time is spent in light sleep with higher probability of waking up. If you’re baby is used to a pacifier, be ready to replace the paci multiple times per night since they’re still too small to do it.

• Keep the room dark – Newborns and infants are not afraid of the dark. They are however, responsive to light. Light tells our brains that it’s time for activity and alertness, and the brain secretes hormones accordingly, so we want to keep the sleep area darkened, eliminating sunlight and possible flashes of light during naps and bedtime.

• …and use white noise – The other nemesis of sleep is noise. With more time spent in lighter sleep, noises can startle baby awake so white noise is a great addition to your nursery.

• Instill a bedtime routine – Bedtime routines should be about 20 – 30 minutes long, and baby should go into their crib while they’re still awake. Feeding should happen first, with whatever calm activity baby likes second and then a diaper change and PJs at the end.

Sleeping through the Night and the Four Month Sleep Regression

If your goal is sleep training after 4 months, our night nurses recommend breaking the milk = sleep association. Here’s what that means:

• Offer breast or bottle when your baby wakes for the day and after naps. Babies are naturally hungry then of course, and feeding while they’re most alert gives their bodies plenty of time to digest before the next sleep.
• Include a feed at the start of the 20-30 minute bedtime routine. This way the bottle isn’t the last step before sleep and baby will not be using milk as their tool to getting to sleep. Feeding at the beginning of the wind down routine also guarantees you a diaper change, and a clean diaper right before baby goes down for the night.
• If baby always falls asleep while feeding, they’ll associate bottle or breast with sleep, making it harder to learn how to fall asleep on their own.

 Note: With newborns, you can’t prevent them from nodding off at the breast or bottle — and that’s okay. As babies get older, they naturally stay awake for feeds, which makes this routine possible.

Four month old infants typically go about two hours between snoozes, with bedtime between 7 and 8 at night. Once babies graduate from the four month sleep progression, they follow the sleep patterns they’ll have for the rest of their lives…four stages repeated multiple times a night! Of course, you may have to sleep train to fully help them sleep through the night if that’s something you want to do, you can follow this infant sleep training guide.