Does your baby wake every 40-50 minutes? Do you find yourself rocking/nursing/bouncing your baby all night long? If this is you, I promise that you’re not the only one. I talk to mommas every day that tell me this exact same thing: “My baby doesn’t sleep longer than 40 minutes at a time”; “I have to hold my baby all night long for them to sleep”; “I think my back is going to give out because I am having to bounce my baby all night long”. What’s going on here? To fully understand what is causing your baby to wake every 40-50 minutes throughout the night you first have to understand your baby’s sleep cycle. Understanding your baby’s sleep cycle changes how you view and approach your baby’s sleep. Today I am going to explain what a sleep cycle is, the phases of a baby’s sleep cycle, why it’s important for your baby to fall asleep on their own, and how baby sleep cycles differ from our own. 

What is a Sleep Cycle? 

A sleep cycle is a (4) phase cycle that babies go through while they are sleeping. These phases are a combination of Non-REM (Non Rapid Eye Movement) and REM (Rapid Eye Movement) sleep. Each phase is unique in itself. These cycle is repeated all night long until it’s time to wake up for the day. Let’s go into more detail of what a baby’s sleep cycle looks like and what is happening in each phase of your baby’s sleep. 

What are the Phases of a Baby’s Sleep Cycle?

There are four stages in a baby’s sleep cycle including: (1) Non-REM, (2) Non-REM, (3) Non-REM, and (4) REM. Let’s break each phase down so you can fully understand what is going on when your baby is asleep. 

Non-REM (Phase 1)

This first phase of sleep is very light. This phase is a very intense stage of relaxation. Your baby’s eyes are closed, but they wake easily in this first phase. Any noises or sudden movements in their environment can awaken them. For adults we can compare this stage of sleep in our babies to our own for example when we are on the couch nodding off to a movie or reading a book. It is the phase between being awake and asleep, but leaning more towards sleep. This stage typically lasts around 5-10 minutes. 

Non-REM (Phase 2)

Your baby is now reaching “sleep status” in this second phase of the sleep cycle. The heartbeat is slowing down, your baby’s body temperature begins to drop slightly and the muscles begin to relax. We are not quite to “deep sleep” in this phase, but very close. This phase lasts around 10 minutes. 

Non-REM (Phase 3)

Your baby is now considered to be in “deep sleep”. In this stage it is very difficult to wake your baby. Their body is completely relaxed at this point in the sleep cycle and their body temperature and heartbeat are considerably lower. Unfortunately I see cases all the time of parents that think this is the appropriate time to lay the baby down for sleep. While most parents think their bliss moment has finally arrived, it is bound to be short lived. Usually you do get your baby down in their crib, but typically what you will find is your baby waking in the next 20-30 minutes after laying them down in this phase. (More on that later and why this is the wrong time to lay your baby down.) This phase lasts around 10-15 minutes. After this phase a new cycle starts and the sleep becomes very light again! 

REM (Phase 4)

Your baby is now in REM sleep which stands for Rapid Eye Movement or also called “active sleep”. During this phase your baby is now back to light sleep and wakes easily during this phase. Your baby’s mind is actively processing and learning in this phase. If you could see your baby’s eyes during this phase you would see how active the mind truly is during this phase. The eyes move very fast, faster than you could move them when awake! That’s what gives the name “Rapid Eye Movement”. In this phase it is very common for your baby to appear awake, talk, move around, etc. due to all the activity going on in their brain. Since REM is a very light stage of sleep most babies do actually wake up, check their surroundings and then if taught they are able to connect another sleep cycle and repeat. This phase lasts around 10 minutes long. 

In total, a baby’s sleep cycle (phase 1-4) is around 40-50 minutes long. 

Why is it Important for Your Baby to Start Falling Asleep on Their Own?

Let’s go back to my initial question, “Does your baby wake every 40-50 minutes?” First of all let’s get something straight, based on the science of a baby sleep cycle every baby wakes after each sleep cycle. The difference between having to intervene to help your baby and not having to intervene (and honestly not even knowing your baby has woken up and put themselves back to sleep on their own) is if your baby knows how to self soothe into the next sleep cycle on their own. Where is this determined within the sleep cycle? At the very beginning! However your baby falls asleep initially is how they will connect each sleep cycle following the first. For instance, if your baby is rocked to sleep and you lay them down already awake then once they reach REM sleep and wake up they will not know how to connect another sleep cycle without being rocked to sleep. This goes for feeding to sleep, bouncing to sleep, and any other form of soothing that involves something outside of your baby’s crib. For your baby to sleep longer and connect sleep cycles on their own they first have to fall asleep on their own. That’s how it works. 

How Baby Sleep Cycles Differ From Adult Sleep Cycles?

The main difference between baby sleep cycles and adult sleep cycles is the time duration in each phase. Where a baby’s sleep cycle is 40-50 minutes long, an adult’s sleep cycle is 120 minutes long. Another key difference is that ratio of Non-REM to REM is completely different in baby sleep cycles than in adult sleep cycles. Babies spend more than TWICE as much time in REM sleep and much less time in Non-REM sleep. Meaning that babies are in “active sleep” much more than adults. It takes years before our baby’s sleep cycles start to look more like ours. It is only when children reach school age that their sleep cycles approach ours lasting around 90 to 100 minutes. Even by the time your baby is 3 years old they still spend 50% of the time in REM sleep whereas adults are only in REM sleep 20% of the time. It is natural for your baby to wake more than you do in the night based on the science behind their sleep cycle. 


I hope this blog answered a lot of questions you have had about your baby’s sleep and how it works! Hopefully understanding your baby’s sleep cycle gives you some kind of peace in knowing what really is going on. But before I end this I need to address the response I know many of you are having in your head from everything you just read. Some of you are thinking, “Well that’s never going to happen! I am not letting my baby cry it out! There is just no way my baby could fall asleep on their own.” I know it’s hard to believe, but I promise you their is a way and it doesn’t involve letting your baby “cry it out”. As your pediatric sleep consultant I give you the gentle methods that allow you to be part of the process of your baby falling asleep and the support you need throughout the process. If this is where you are struggling and don’t know the next steps PLEASE message me or sign up for a free consultation on my website! You don’t have to feel alone in this journey of sleep! I will walk you through every step! Let’s do this together and help your little one learn how to connect sleep cycles and find rest!