If you follow our series on the first year of a child's life, you know we have been through it all - from sleepless nights to first steps. And if there is one thing we wish someone had explained to us at the very beginning, it is developmental leaps. Because when a baby who was all smiles yesterday suddenly becomes weepy, restless and stuck to you like Velcro, the first thought is: "What did we do wrong?" The answer, most of the time, is - nothing. Your baby is just growing. Quite literally: her brain is getting an upgrade.
In this article we walk through all ten developmental leaps: when they come, how to recognise them, which one is (in the experience of most parents, ourselves included) the worst, and what to do when you are in the middle of one.
🍼 Get your baby's leap dates
What are developmental leaps?
The concept of developmental leaps is best known from the book The Wonder Weeks by Dutch researchers Frans Plooij and Hetty van de Rijt. Observing babies and their mothers, they noticed that periods of fussiness and crying appear at predictable intervals - and that after each such period the baby suddenly shows new mental abilities.
The idea is this: a baby's brain does not develop evenly, but in sudden leaps. Each leap brings a new way of perceiving the world. Imagine waking up one morning suddenly able to see colours you could not see yesterday. Fascinating? Yes. But also quite confusing and scary. That is (figuratively) exactly what happens to the baby. Her familiar, predictable world suddenly looks different, and the only safe place in that new chaos is - you.
That is why a leap is easiest to recognise by the three C's: crying, clinginess and crankiness. The baby wants to be carried more, sleeps worse, eats worse and generally lets you know that nothing is to her liking. And then, after a few days or weeks, the storm passes - and the baby suddenly shows something new. She follows your gaze, reaches for a toy, understands "where is the ball?". That is the reward at the end of every leap.
One more important thing: leaps are counted from the due date, not the birth date. If your baby was born three weeks early, expect the leaps about three weeks "later" than the calendar says. For babies born close to term, the difference is negligible.
And to close this introduction, a caveat we consider important: the scientific community is not unanimous on whether the leaps land exactly in the listed weeks for every baby. Attempts to replicate the original research have produced mixed results. Our experience? The order and the descriptions of behaviour were surprisingly accurate, while the exact weeks sometimes ran "late" or "early". So treat the leap calendar as a useful guide, not a strict schedule.
Developmental leaps chart
Here is an overview of all ten leaps. Weeks are counted from the due date:
| Leap | Week | Approximate age | What the baby discovers |
|---|---|---|---|
| 1 | Week 5 | 1 month | The world of sensations |
| 2 | Week 8 | 2 months | The world of patterns |
| 3 | Week 12 | 3 months | The world of smooth transitions |
| 4 | Week 19 | 4 - 5 months | The world of events |
| 5 | Week 26 | 6 months | The world of relationships |
| 6 | Week 37 | 8 - 9 months | The world of categories |
| 7 | Week 46 | 10 - 11 months | The world of sequences |
| 8 | Week 55 | 12 - 13 months | The world of programs |
| 9 | Week 64 | 14 - 15 months | The world of principles |
| 10 | Week 75 | 17 - 18 months | The world of systems |
The fussy phase usually starts a week or two before the listed week and lasts anywhere from a few days to a few weeks, depending on the leap (and on the baby!).
Leap by leap: what to expect
Leap 1 (week 5): the world of sensations
The first leap arrives as early as week 5. The baby's sensory organs mature rapidly - suddenly she sees, hears and feels more intensely than before. For the baby this is overwhelming, so no wonder she is weepier and wants more cuddling. The good news: after this leap many babies show their first real social smile, and parental happy tears are guaranteed. We wrote more about this period in our article on the first month of a newborn's life.
Leap 2 (week 8): the world of patterns
Around week 8 the baby starts recognising simple patterns - repeating shapes, sounds and movements. Suddenly her own little hands are the most fascinating thing in the world and she can study them endlessly. Experimenting with sounds begins too. What that looks like from a parent's perspective, we described in our article on the second month of life.
Leap 3 (week 12): the world of smooth transitions
Around week 12 the baby starts noticing subtle, continuous changes - how a voice rises and falls, how an object approaches. Her own movements become smoother and more controlled as well. This is the period of cooing, "conversations" and the first real laugh out loud. We covered all the news of the third month in this article.
Leap 4 (week 19): the world of events
Now. Take a deep breath. The fourth leap, around week 19 (so between the fourth and fifth month), is for most parents the most demanding - so much so that we dedicate a separate chapter to it below. The baby begins to understand that actions consist of sequences of events: the ball drops, bounces and rolls away. After the leap the baby starts reaching for objects, passing them from hand to hand and putting everything (and we mean everything) into her mouth. We described the details in our articles on the fourth and the fifth month of life.
Leap 5 (week 26): the world of relationships
Around week 26 (month six) the baby discovers relationships between things - what is near, what is far, what is inside, what is outside. And most importantly of all: she realises that distance applies to you too. Mum can leave. That is the beginning of separation anxiety, which will keep coming back in waves for a long time. A baby who until now sat happily with grandma suddenly screams the moment you leave the room. Exhausting? Yes. But also a sign of healthy cognitive development. More in our article on the sixth month of life.
Leap 6 (week 37): the world of categories
Around week 37 the baby starts grouping the world into categories: a dog is a dog, whether big or small, black or white. This is the foundation for learning concepts and, later, speech. During this period the baby explores everything intensely - squishes food, tears paper, compares. You can read about our experiences from that time in our articles on the eighth and the ninth month of life.
Leap 7 (week 46): the world of sequences
Around week 46 the baby figures out that things are done in a certain order: first the spoon goes into the bowl, then into the mouth. She starts stacking blocks, putting objects into boxes and taking them out again (a hundred times in a row). This is also the period of the first real participation in daily routines. What that looks like in practice, we wrote in our articles on the tenth and the eleventh month.
Leap 8 (week 55): the world of programs
The leap around month 12 (week 55, to be precise) brings an understanding of "programs" - flexible sequences of actions with a goal. Washing dishes, getting dressed, going to the shop - the child begins to grasp these larger wholes and wants to take part in everything. This leap often coincides with first steps and first words, making the period around the first birthday a real fireworks display of new skills. More in our articles on the twelfth month and the thirteenth and fourteenth month of life.
Leap 9 (week 64): the world of principles
Around week 64 (14 - 15 months) the child starts thinking about her own thinking - sounds abstract, but in practice it means: she plans, negotiates and tests boundaries. Yes, at 15 months. She begins to understand "mine" and "yours", experiments with "yes" and "no" and for the first time deliberately provokes to see your reaction. The first tantrums often start right about now. How we survived it, read in our article on the fifteenth and sixteenth month of life.
Leap 10 (week 75): the world of systems
The last "official" leap arrives around week 75, that is around months 17 and 18 - and many parents remember this one as among the stormier ones. The child begins to understand systems: the family is a system, home is a system, "us" and "them". Self-awareness develops - the child recognises herself in the mirror, starts talking about herself and shows the first traces of empathy and conscience. On the other hand, her will grows stronger too: the child knows exactly what she wants, and your schedule is often not part of the plan. The combination of the leap, molars coming in and a growing need for independence can make the period around month 18 quite intense. We described it in detail in our article on the seventeenth and eighteenth month of life.
Which developmental leap is the worst?
This is the most searched question and the one most discussed on parenting forums. There is no official answer - every child is different. But the unofficial parental consensus (and our personal experience) is quite clear: leap 4, around week 19, that is around the fourth month of life.
Why that one? A few reasons:
- It is the longest. The fussy phase of leap 4 can last up to 5 - 6 weeks, while the first leaps pass in a few days.
- It coincides with the 4-month sleep regression. Around the same time the architecture of the baby's sleep changes permanently - the baby starts sleeping in cycles more similar to adults', with more wake-ups in between. Leap + sleep regression = zombie parents.
- It comes right after the "honeymoon". Around month three most babies become calmer and more predictable, so parents just start thinking "we've figured out the system". And then - boom.
Right behind it, parents most often mention leap 8 (around month 12) and leap 10 (around 18 months), where the mental upgrade combines with walking, teething and an ever louder "NO!".
If you are currently in the middle of the worst leap: hang in there. It passes. And on the other side, a baby who can suddenly do a whole set of new things is waiting for you.
Leaps after 18 months: 22 months, age 2 and age 3
The Wonder Weeks calendar officially ends with leap 10 around week 75. Does that mean it is all smooth sailing after month 18? Every parent of a two-year-old just laughed out loud.
Development, of course, continues - we just no longer describe it in weeks but in phases. Around month 22 many children go through an intense period of boundary testing and an ever stronger need for independence ("I DO IT MYSELF!"), which we wrote about in our article on months 21 and 22. At age two the famous autonomy phase arrives (known as the "terrible twos", though we prefer to call it the phase of the little scientist testing every single hypothesis) - all about it in our article on the two-year-old child. And at age three comes a great expansion of speech, imagination and social skills, with the occasional dramatic meltdown because the banana was cut the wrong way. More in our article on what to expect from a three-year-old.
So: leaps in the strict sense stop around month 18, but stormy periods after which the child suddenly "grows up a notch" will follow you for years. The good news is that you grow more experienced too, so nothing can surprise you anymore. (Almost nothing.)
How to survive a developmental leap?
A few things that helped us, leap after leap:
- Lower the bar. A week in which the baby will not sleep and wants to be carried constantly is not the week for spring cleaning and ambitious plans. Survival is success.
- Give the baby what she asks for - closeness. A leap is a confusing time for the baby, and you are her safe base. Carrying, cuddling and extra feeds will not "spoil" her; they help her feel safe while her world is changing.
- Stick to the routine as much as you can. When the baby's inner world is in chaos, a predictable outer world means a lot.
- Offer new activities after the leap. Once the fussiness passes, the baby is hungry for new experiences - it is the ideal time for new games and activities that encourage development.
- Share the load. Take turns with your partner, accept help from the grandparents. Leaps are a marathon, not a sprint.
- Remember: fussiness is a sign of development, not of a problem. A baby crying through a leap is not "naughty", nor are you doing something wrong. Her brain is simply working overtime.
And most importantly: if something seriously worries you - the baby is not gaining weight, is losing skills she already had, the crying sounds different than usual - talk to your paediatrician. Leaps explain a lot, but they do not explain everything.
Frequently asked questions about developmental leaps
Which developmental leap is the worst?
Most parents consider leap 4, around week 19 (between the fourth and fifth month of life), the hardest. It is the longest of all - the fussy phase can last 5 to 6 weeks - and it coincides with the 4-month sleep regression. Right behind it, parents often name leap 8 around the first birthday and leap 10 around 18 months.
When is the 18-month developmental leap and how long does it last?
The tenth leap starts around week 75, that is around month 17, and the fussy phase can last several weeks. The child discovers the "world of systems": develops self-awareness, recognises herself in the mirror, shows the first signs of empathy - but also a very strong will of her own. It is the last leap in the Wonder Weeks calendar.
How can I tell my baby is going through a developmental leap?
The most common signs are the three C's: crying, clinginess and crankiness. The baby wants to be carried and cuddled more, sleeps worse, eats less and is hard to please, with no signs of illness. After a few days to a few weeks the fussiness passes and the baby shows new skills.
Are leaps counted from the birth date or the due date?
From the due date. Leaps follow brain development, which starts at conception, so the calendar is counted from the date the baby was supposed to be born. If your baby was born three weeks early, expect the leaps roughly three weeks later than the chart says.
Is there a developmental leap at age 2?
According to the Wonder Weeks calendar, the last leap ends around month 18, so there is no "official" leap at age two. But development continues in stormy phases: around the second birthday the autonomy phase begins (also known as the "terrible twos"), with intense boundary testing and a strong need for independence. In intensity, it certainly feels like a leap.
Is there a developmental leap at age 3?
Formally no, but around the third birthday there is a great expansion of speech, imagination and social skills, often accompanied by strong emotions and the occasional tantrum. Many parents describe the third year as more demanding than the second, which is why people jokingly talk about "threenagers".
Do leaps last the same for every baby?
No. The order of the leaps is the same for all children, but the intensity and duration vary a lot - one baby gets a leap "done" in a couple of grumpy days, another turns the house upside down for three weeks. If the baby was born before term, the leaps come later. So treat the calendar as a guide, not a strict schedule.
We hope this guide helped you put the current (or upcoming) chaos into context. And if you are wondering what else awaits you in each particular month besides the leaps, there is our month-by-month series - from the first month of a newborn's life all the way to age three. Good luck, and remember: every leap passes. And every one brings something wondrous.
