Wonder Weeks leap guides: weeks 4 to 75

For general reference only, not medical advice. Every baby develops at their own pace. If you are worried about your baby, contact a doctor or other health professional.

Many parents notice that their baby goes through short spells of extra crying, clinginess and broken sleep, followed by calmer periods with new skills. The Wonder Weeks model groups these spells into ten windows during roughly the first twenty months, counted from the due date. The calculator on this site marks those windows on a personal calendar.

The guides below explain each window in plain language: when it usually falls, what parents commonly notice, what is developing, practical ways to help and the signs that mean you should contact a doctor rather than waiting. Babies vary a great deal, so treat every date as an estimate.

Why the dates are counted from the due date

Development in the first months follows the maturity of the brain and nervous system more closely than the number of days since birth. That is why the windows are counted from the due date. If your baby was born early, enter the original due date in the calculator and the windows will move later accordingly. Health professionals use the same idea, called corrected age, for early milestones.

All ten guides

1. Leap 1 Weeks 4–5 · about 1 monthMore crying in the evening, wanting to be held and frequent feeds as the senses become sharper.
2. Leap 2 Weeks 7–9 · about 2 monthsShorter naps and quick overload while your baby starts to notice hands, voices and repeated routines.
3. Leap 3 Weeks 11–13 · about 3 monthsKicking, swiping and reaching improve, but your baby still struggles to notice their own tiredness.
4. Leap 4 Weeks 15–19 · about 4 monthsOften the longest early window, with sleep changes, rolling practice and distracted feeding.
5. Leap 5 Weeks 23–26 · about 6 monthsYour baby starts to notice distance and separation, so short goodbyes can feel bigger.
6. Leap 6 Weeks 34–37 · about 8 monthsYour baby sorts people and things into groups, so strangers and separations stand out more.
7. Leap 7 Weeks 42–46 · about 10 monthsYour baby learns that actions come in an order, so interruptions can lead to big protests.
8. Leap 8 Weeks 51–54 · about 12 monthsAround the first birthday, your child wants to do more alone but still needs reassurance.
9. Leap 9 Weeks 60–64 · about 14 monthsYour toddler copies adults and makes small plans, but cannot yet explain every need in words.
10. Leap 10 Weeks around 75 · about 17 monthsYour toddler has strong opinions and begins to notice other people’s feelings and rules.

Signs that always need a doctor

Whatever the calendar says, seek urgent medical help for difficulty breathing, blue or very pale lips or skin, a baby who is unusually floppy or hard to wake, a seizure, a rash that does not fade when pressed, signs of dehydration such as very few wet diapers, repeated forceful vomiting, or a fever of 38°C (100.4°F) or higher in a baby under three months. Trust your instincts: if you feel something is wrong, contact a doctor or emergency service.