Welcome to the module on Sleep Science. This module explains why the Simplicity Sleep programme works! This course is very much grounded in the science of sleep, or sleep biology, as it’s sometimes known. In this module I’ll be discussing what we know about sleep biology and baby/toddler sleep. The suggestions throughout this course aim to work with your baby’s natural ability to sleep. While this module focuses mostly on sleep biology, throughout this course, I’ve also integrated knowledge from attachment theory, anthropology, child development, and neuroscience. These disciplines complement the hard science of sleep biology, to provide an evidence-based framework for improving sleep.

When you go through this module, you’ll probably realize that babies actually sleep quite differently from us, as adults. You may also realize that babies sleep differently from what our society expects them to. So you might find that your expectations of child’s sleep might change as you go through this module. That might not be a bad thing. Remember, this course is about finding the easiest route possible to improving sleep for your family. Once you know what your baby is capable of (or not), it might make more sense to focus on the Simple Sleep solutions and Sleep Shaping rather than to move towards Sleep Strategies. Around half of babies have improved sleep with just the Simple Sleep solutions and Sleep Shaping, and there is usually a lot less effort involved with just those changes. The Sleep Strategies often involve much more work and effort.

Normal sleep – video

** Please note that there is an error in the video – the average number of naps between 12 and 18 months is 1-2**

Let’s look at the averages!

Let’s look at normal sleep for babies up to the age of 18 months. Some of the information in my chart is based on big studies that have looked at averages for babies and toddlers. There are some figures on this chart that I can say fairly confidently are evidence based. The total sleep in 24 hours is probably the most reliable figure, and then there is some fairly good evidence for the total hours that they spend sleeping during the day versus how much they sleep at night time. I should point out that “research based” does not necessarily mean that this is what happens across the world, in all societies – this is merely normal for a Western society, because that is where most of the research has happened. I should also point out that there will always be some babies that fall outside of the average ranges – this usually isn’t something to worry about.  

There is very little research on the number of naps babies should take, and very little research on what is called their “wake window” – that period of time they can tolerate being awake before they need to sleep again. So for these columns on my chart I’ve looked at what is written in sleep books and I have also incorporated knowledge and experience I’ve gained working as a sleep coach – more “empirical” rather than research based knowledge. These are the columns where we have to take a more flexible approach because there isn’t actually any science on this, to be honest. So if your baby is falling way outside the averages for naps or awake windows, I’d not be too worried. Look at the total amount of sleep – how does that look? Sometimes if you’re really struggling with sleep at night time, you do actually need to work outside the averages and I’ll talk about that in the Sleep Shaping module. 


If you’ve looked at the chart and it doesn’t look like your baby is within an average range, there are a few things to check first of all:

  • Are you counting all the sleep your child is getting? I’d count those fluttery sucks at the end of the feed as sleep, as well as those 5-10 mins where they are lying on your shoulder sleeping before you put them down. If a baby wakes for 5-15 minutes at night time, I’d not count that as being awake. Usually you can count the time that they go down for the night and when they wake up for the day as night sleep, ignoring those “micro-wakes”. If your baby is up for an hour long party at 2 am, then you can definitely take that hour off the total sleep!
  • Is your baby getting enough sleep in 24 hours? A lot of babies do fall at the lower end of the sleep averages – especially the ones I see as clients. Some babies just have lower sleep needs. What are you like? Do you need less sleep than average? Could it be genetic?
  • What is your baby like during the day? Happy, content? Or grumpy, yawning, rubbing his/her eyes? Often babies with lower sleep needs seem completely fine during the day, and unaffected by less sleep.
  • Have you ruled out any medical issues that might be affecting sleep? Is your baby gaining weight well? Are they snoring frequently? Is there eczema that might be causing discomfort at night time?

Still not sure? Fill out a couple of days of sleep diaries (in your workbook) – then add them up again. If you want me to take a quick look at them for you, send it through to me at

The roller coaster of sleep

I think it’s important to address our expectations of babies’ normal sleep because I think a lot of our frustration as parents stems from this idea that babies should start sleeping through the night fairly early on. I think most of us accept that newborns are probably not going to sleep great. I think we know that, but somewhere in the back of of our minds we think that sleep gradually improves and then it stays good for the rest of the baby’s life. Unfortunately that isn’t true. Sleep is probably about as good as it’s going to be at around three months. Some parents say that sleep goes downhill at around 4 months and stays bad for months, other parents find that it’s a bit more up and down than that, with sleep being the worst that it will be between 8 and 10 months, before gradually starting to improve again.

You’ve probably heard of sleep “regressions”. It’s not really accurate to label them as regressions, because these periods of disturbed sleep are a normal part of child development. A regression, in medical terms, is when a child reaches a developmental milestone and then loses that ability. That is always a red flag. So for example, if a baby starts sitting up and then can’t do it any more, you’d want to take that baby to the doctor. Or if a toddler has started saying words, and then stops speaking, that would be a red flag too. However, when sleep gets worse, where previously a baby has been sleeping well, that’s not a regression in the true sense. When we understand what’s going on with sleep cycles and developmental changes during that first year, we start to understand WHY sleep becomes disturbed. It’s not a regression, it’s developmental. Some positive, enthusiastic sleep coaches call them progressions, but I’d not go that far. I’d say it’s more that disturbed sleep is the collateral damage resulting from other developmental changes. Typically, parents would say that sleep gets worse around 4, 6, 8-10, 12 and 18 months. Reasons why babies experience disturbed sleep include:

At around 3 months, the total amount of sleep babies need drops – they go from needing around 14-17 hours to around 12-15 hours. Sometimes parents find it hard to make that adjustment and accept that babies need less sleep in total.

Sleep cycles change at around 3-4 months (more about that shortly)

Starting solids – constipation, digestive issues, potential allergies can all affect sleep. As I’ve mentioned before, filling a child up with food (especially before bed) isn’t going to improve sleep.

Becoming more mobile – there is research showing that the consolidation of learned physical skills such as rolling, sitting, crawling, cruising and walking happens at night time and that the periods of time where a baby is learning a new skill often results in disturbed sleep.

Teething – this is often blamed for weeks of disturbed sleep, but usually if teething is going to affect a child it only affects them for 2-3 days as a tooth is erupting. This is a long read, but it’s probably the best research based explanation of teething that I’ve found: Teething – is it as bad as the horror stories? – Holistic Sleep Coaching.  If your baby is constantly cranky and crying at night time – there is something else going on that is bothering them.

Separation anxiety – common at around 8-10 months and again at 16-18 months. The first cycle of separation anxiety also often corresponds with the primary caregiver going back to work after maternity/paternity leave.

Dropping naps – you may not notice the effect when your baby goes from 5 to 4 naps, but the drop from 3 to 2 naps and from 2 to 1 nap often results in disturbed sleep for 2-3 weeks as the child adjusts. The awake window becomes proportionally bigger the less naps a child has. Check out the troubleshooting module for ways to ease that transition when dropping a nap.

Frequent colds and infections – this is probably less common with covid restrictions in place, but it wouldn’t be unusual for a young child to have 10 or more colds in a year. The resulting nasal congestion, sore throat, coughing and general discomfort is often worse at bedtime. Sometimes frequent colds can cause swollen adenoids and tonsils, resulting in regular snoring and mouth breathing (remember, that’s a RED FLAG and needs to be checked by your GP).

Unrealistic expectations – there is a maximum number of hours that a baby can sleep. If parents are expecting long naps during the day, plus a 12 hour stint in bed, often babies wake up more during the night because sleep pressure isn’t high enough. (We discuss this in more detail in the Sleep Shaping module). Parents may also want their babies to fall asleep on their own, or sleep in their own room, or significantly reduce night feeds. Some babies adapt very quickly to these changes, but some babies struggle with this.

Sleep cycles

When our babies are born, they have a very different sleep cycle from the way we have sleep as adults. Newborns have a fairly simple sleep cycle, it lasts between 40 and 50 minutes and they actually spend half of their time in light sleep, but most of this is REM (rapid eye movement) sleep. REM sleep can be described as active sleep, and non-REM (NREM) sleep as quiet sleep. So newborn babies fall asleep via REM sleep, spend maybe 10-15 minutes in light, active sleep, then move into deeper sleep for maybe 20 minutes, and then back into REM sleep. After this second period of REM sleep, their sleep cycle comes to an end and they often wake up. So if your newborn is only sleeping for 40-50 minutes at a time and then they wake up again, that’s completely normal. Sometimes if the conditions are right, if they are sleeping on you, or they’ve started to establish their circadian rhythm at night time, they will be able to link their sleep cycles. So for example, if a baby sleeps two hours, they don’t have a 2 hour sleep cycle, they are probably linking 2-3 sleep cycles.

Adult sleep cycles are different. They last 90-120 minutes, and we fall asleep via light sleep that is NREM, then our sleep gets progressively deeper throughout the sleep cycle, and then we finish that sleep cycle with a short episode of REM sleep. Often, adults will stir at the end of a sleep cycle and then fall asleep again, much like babies do! We just don’t need help to fall asleep again.

At around 3-6 months, babies start to fall asleep via NREM sleep, much the way we do, and they start to develop the different stages of NREM sleep too. This probably accounts for some of the disruption that happens at that so called four month sleep regression – this change in the way sleep happens causes more waking. A lot of parents will also say that their baby starts to become more aware of falling asleep and fights it, whereas when they were newborns they would just fall asleep spontaneously – this is probably because babies start falling asleep via NREM sleep, rather than REM sleep.

We don’t know at what stage a child’s sleep cycle becomes exactly the same as an adult’s sleep cycle, in terms of the different stages and length. It probably varies from child to child, but may happen as early as toddlerhood for some. You’ll find that as your child gets older, their sleep cycle gradually gets longer. So by the time they are a year old, you may find that their sleep cycle is closer to an hour, and that this gradually gets longer as they get older.

It’s also important to realize that the way sleep happens, changes as the night progresses. As the night goes on, your sleep becomes lighter, your sleep cycles become shorter and you experience more REM sleep. This is also true for babies once they have started to develop a more adult sleep cycle. This may explain why babies wake more frequently in the early hours of the morning, and if you are bedsharing, you may also be more aware of your baby stirring (and feeding!) more frequently at this time.

It is very normal for babies to wake frequently at night time. If you have a friend who tells you that her little boy is sleeping through the night – I can guarantee you that he isn’t! He most certainly is stirring at certain times during the night, but for whatever reason, is able to go back to sleep. Just like your baby, he is stirring at the end of a sleep cycle. If your baby needs help to go back to sleep at the end of each sleep cycle, that is really, really hard. I’m not going to pretend that it’s easy, or that you should just accept it and do nothing. This course is about finding a balance – accepting that our babies will still need us at some points during the night, but also finding solutions so that we (as parents) can still get decent blocks of sleep during the night.


Babies have a lot more REM sleep than adults do. This may be developmental, as mammal babies that are born immature and more helpless exhibit more REM sleep than mammal babies that are born mature and able to look after themselves. It would appear that REM sleep is actually involved in helping brains develop rapidly. So for babies, this light active sleep is good! It helps the brain develop.

Furthermore there is some evidence that REM sleep helps to develop that emotional centre in our brains – the part that is involved in love and bonding and relationships. Babies exhibit more REM sleep when in close proximity to a care giver – so co-sleeping may actually help to strengthen their emotional brain.

Source: Gethin and Macgregor, Helping Baby Sleep, 2009

Video – circadian rhythm and sleep pressure

Circadian rhythm

Hopefully by now you’ll have some idea of what the circadian rhythm is, as I’ve mentioned it briefly in the Simple Sleep Solutions. We’re going to look at it in a bit more detail now.

Your circadian rhythm is basically an internal clock that let’s you know when it’s time to get up, and when it’s time to go to bed. It is very much influenced by light and by routines. Where babies are concerned, it can take 3 months for newborn babies to fully develop a circadian rhythm. Furthermore, because babies don’t often settle in to a pattern of naps until they are over 3 months, the routine part of a circadian routine doesn’t apply to very young babies. Once they are on regular naps, then you can try to keep the naps timings fairly consistent from one day to the next. It’s important that babies are fed responsively while they are still on milk feeds. The routine part of eating really only comes into play once they are on solids and then meals can be scheduled at roughly the same time every day. This is important to do, because we actually have internal sensors in our gut that react to regular timings and they can be powerful triggers for setting our circadian rhythm and signaling when it’s time for sleep. However, milk feeds should always be flexible and responsive, especially while milk is a baby’s main source of nutrition, which is usually till around a year. So, since babies don’t develop consistent naps until they are around 3 months, and because they don’t start solids until around 6 months, there really isn’t much point in going for rigid routines – they just don’t work for most babies, especially young babies. In fact, trying to stick to routines may actually cause more harm than good, especially to your confidence in parenting – you can read more about this here.

Let’s look at the other aspect of your circadian rhythm and how it’s controlled by hormones, in response to light. You have two main hormones that help “set” your circadian rhythm. You’re probably already familiar with melatonin, which is the sleepy hormone produced a couple of hours before bedtime. It is produced in response to fading light, and helps us fall asleep and stay asleep overnight. It peaks in the early evening and then gradually falls overnight, so that melatonin levels are at their lowest in the early hours of the morning.

However, there is another hormone at work, which is cortisol. You may know cortisol as a stress hormone, and yes, in excessive levels, cortisol can be damaging, especially to healthy brain development. This is one of the arguments against cry it out methods of sleep training – there is some evidence that babies who are left to cry it out secrete elevated levels of cortisol.  However, cortisol secretion is also part of our circadian rhythm, we do want our bodies to produce some cortisol! Cortisol levels are usually highest first thing in the morning – consider it your “get up and go” hormone – it wakes you up and makes you feel alert. Cortisol levels then fall throughout the day and are at their lowest at bedtime. This is why if your baby has eczema or dermatitis, the itch is going to be much worse at bedtime (cortisol actually helps to reduce an itch).

You can strengthen your child’s circadian rhythm by exposing them to lots of daylight, as this ensures that melatonin production happens at bedtime. As I’ve mentioned before, you don’t really want your child to be spending too much time in a dark room during the day because you don’t want them to make melatonin in response to that dim light, you really only want them to be making melatonin at night time. Around 2 hours before bedtime you want to start dimming the lights and avoiding the use of screens. That will trigger the production of melatonin so that when you get to bedtime, melatonin is actually going to be at its highest levels and if bedtime is timed right, it is usually fairly easy to fall asleep.

You can also strengthen your baby’s circadian rhythm by having a consistent wake up time and consistent bedtime. You may find that your bedtime varies over time – remember, younger babies tend to spend less time in bed overnight so their bedtime may be later than a toddler’s, especially if everyone in the family is getting up at the same time every morning.


NAPS – after three months, once you see a regular pattern emerging naturally – more details in the Sleep Shaping module

FOOD – after six months, with regular meal times

MILK – only when they don’t rely on it for main source of nutrition (usually over a year)

Sleep pressure

The next thing we’re going to look at is the difference between circadian rhythm and sleep pressure. Circadian rhythm is your internal body clock and it helps you sleep at night time. Sleep pressure is basically just how tired you are, and how quickly you get tired. So if we think about wake windows, these are basically the time your child can tolerate being awake before sleep pressure gets too high. When babies are newborn they probably are only going to have a wake window of about 45 minutes because the sleep pressure builds really quickly with them. They need to sleep more often. As they get older it takes longer for that sleep pressure to build. So by the time your baby is nine months they can maybe go two or three hours between naps.

By the time you get to bedtime, your sleep pressure should be high, and that, coupled with your circadian rhythm, helps you and your baby fall asleep and hopefully stay asleep! If your baby has had lots of sleep during the day then their sleep pressure isn’t going to be terribly high at bedtime and conversely if they really haven’t slept much during the day then the sleep pressure is going to be really high at bedtime. Neither of these scenarios is ideal, so it’s about getting the balance right for your baby, and we’ll talk about that in a lot more detail in the Sleep Shaping module, but here’s a brief introduction:

As a general rule of thumb, it’s often the gap between the last nap and bedtime that has the biggest impact on night sleep. This is because the level of sleep pressure at bedtime is dependent on how much sleep pressure has built up between the last nap and bedtime. If your baby wakes up in the morning and they’ve had a good night’s sleep, you can assume that their sleep pressure is fairly low. As they spend some time awake, their sleep pressure starts to rise. When they take a nap, the sleep pressure falls as they sleep. Here is where nap timings get tricky. If a baby sleeps too long, then sleep pressure falls completely. That means that there will be a longer gap before the baby needs their next nap. If the next nap (or the last nap of the day) isn’t timed right, then babies end up either being not tired enough at bedtime, or too tired. Ideally naps just “take the edge” off sleep pressure, so that it rises gradually throughout the day. When you get your child to bedtime, you want their circadian rhythm to be signaling that it’s time for sleep, and you also want sleep pressure to be just high enough.

What helps sleep pressure build?

Adenosine – a hormone we secrete. Levels rise when we’re awake, prompting feelings of tiredness the longer we’re awake.

Less sleep! The less sleep we’ve had the quicker sleep pressure builds.

Sensory experiences – lots of wonderful sensory experiences will help sleep pressure rise. Think of how much more tired you are after a day at the beach, with the wind, sun, fresh sea air, cold water, compared to a day stuck in doors in front of the tv.

Exercise – kids need loads of opportunities for movement and exercise – the more active they are the quicker sleep pressure will rise. (Exercise can also help “burn of” cortisol levels that have got a big high – see below)

Naps and wake windows

Most children will need to take naps until they are at least 2 years old. The number of naps they need during the day will depend on:

  • Their age – they need less naps as they get older.
  • How much night sleep they get – kids with a longer night in bed might need less time napping during the day, and vice versa.
  • How long their naps last – babies with short “cat naps” will probably need more naps than babies who take long naps.
  • How well they tolerate being awake!

As a general rule of thumb, it’s a good idea to spread the naps out equally through the day. I’d quite often see babies whose naps are quite close together at the start of the day and then there is a big gap between the last nap and bedtime. Night sleep often improves when naps are more equally spread out.

Remember that day sleep happens in a different way from night sleep. It’s ok to make a little bit of noise near your baby during the day, and for them to sleep in a bright room for naps. Remember, naps are there to take the edge of sleep pressure, not necessarily to remove ALL sleep pressure completely. Short naps are ok from a sleep biology perspective. In fact, sometimes long naps reduce sleep pressure too much – I’m not denying that long naps are great for us as parents though! If your child has a short nap, you may be able to resettle them easily after 20-30 minutes, if they haven’t had enough sleep. However, if they decide that they are awake and they “come round” after a few minutes, then don’t persist trying to get them to sleep again, just plan your next nap accordingly.

There is often a trade off between day sleep and night sleep. Babies have a maximum number of hours that they can sleep in a 24 hour period. If your child is having a lot of day sleep, then you might find that night waking is more frequent, they have a short night’s sleep, or they may even have a middle of the night party, where they are awake for an hour or two (called a “split night”). You may decide that you’re ok with longer naps during the day, because it gives you a much needed break, or you may decide that you want better sleep at night, in which case you want to cut down on the day sleep a bit. We’ll look at nap optimizing in more detail in the Sleep Shaping module. It’s worth remembering that babies are individuals and sometimes naps and bedtimes need a bit of tweaking. If you want a little bit of extra support with this, you can book an online clinic slot to look specifically at this.

What happens if you miss a nap?

Honestly, it’s not the end of the world. It can be really frustrating if you like routine and naps happening at the same time every day, but a degree of flexibility is good too. We’ll look at routines and how to help your child fall asleep in much more detail in the Sleep Strategies module. However, for the purposes of looking at the sleep biology behind naps, it can be helpful to think about what happens if you’ve missed a nap, or you’ve exceeded that wake window.

So, say you’ve been out and about and you have missed that opportunity to facilitate sleep – your baby is getting fussy and cranky. Perhaps he/she has produced a little bit of cortisol (that “get up and go” hormone) to keep him/her awake, or their nervous system is a little bit dysregulated. If your child is hyper and fussy, sleep isn’t going to happen straight away, you need to either do some active play to “burn off” the cortisol, or you will need to spend a little bit more time providing some soothing activities to calm them down. So, for example, with an older baby, you might want to do some tickle play, get them laughing to relieve that built up energy and emotion, or chase them around the room! With a younger baby, you might need to add in an extra layer of soothing, so if feeding is usually all you need to help your baby fall asleep, you might find you have to add some rocking and shushing too.

Children who have missed their ideal nap window often go through a cycle of restless, fussy behaviour, then some quiet, calm behaviour (this is a great time to facilitate sleep), and then some restless, fussy behaviour again and then some calm behaviour. So if you do miss that window of opportunity for sleep, just wait 20-30 minutes until that quiet, calm behaviour rolls around again!


I love the concept of sleep onset latency! I find it a really easy tool to help judge whether a nap (or bedtime) is well timed. Sleep onset latency is fairly consistent across the lifespan – basically it doesn’t differ too much from infancy through to adulthood. An average sleep onset latency is 15-25 minutes. So, if it takes you 15-20 minutes to fall asleep, you’re probably falling asleep at the right time. If you fall asleep very quickly, say around in around 5 minutes, you’re probably a bit overtired. If it takes you (or your child) longer than 30 minutes to fall asleep then it’s worth re-thinking your timings. Either sleep pressure hasn’t built enough, or you’ve missed that sleep window, and you’re a little bit overtired.

Video on chronotypes, calm and connect

Biological chronotype

Biological chronotype sounds fancy, but basically just describes whether you are a night owl or an early bird. Almost all children are early birds – often waking long before we’d like to be awake! So, parenting a baby if you are also an early bird tends to be easier. If you are a night owl, then parenting and and dealing with your baby’s sleep becomes a lot harder. There isn’t an awful lot you can do to change the time your baby wakes up (I do cover this is the Sleep Shaping module),  but it might be worth thinking about your own bedtime, and making sure that you get enough sleep so that when 6 am rolls around, it’s not such a huge shock to your system.

Connection and calm

Don’t forget! Your relationship with your child and your ability to soothe them and regulate their emotional state is central to sleep. It’s not just about the cold, hard science. Your child needs to feel connected with you, and completely calm and relaxed for sleep to happen.