🧮 Free Tool
Leap Week Calculator
If your baby has suddenly become unsettled, wants to feed constantly and keeps waking at night, you may be in a leap. Enter the due date and we'll list all 10 leaps of the first two years date by date, and mark which one applies right now.
Leaps are calculated from the due date, not the birth date. Use the due date even if your baby arrived early or late.
Pick the estimated due date to see the calendar.
What Is a Leap Week?
Leap weeks — known in the literature as 'wonder weeks' — are the periods when a baby makes a jump in mental development. The baby suddenly starts perceiving the world in a new way: distinguishing sounds, noticing patterns, grasping that objects don't disappear. That new perception tires the brain and unsettles the baby.
These periods aren't an illness or a regression; they are a sign of development. A leap is usually followed by a new skill: smiling, rolling, sitting or crawling.
What Are Leap Weeks Calculated From?
The most commonly confused point is this: leaps are counted from the **due date**, not from the date of birth. If your baby arrived 3 weeks early, their developmental calendar still starts from the due date.
That's because the jumps depend on brain maturation, and brain development follows its own timetable regardless of when birth happened. This is why the tool above asks for the due date rather than the birth date.
What Are the Symptoms of a Leap?
The three most common signs are often summed up as the 'three Cs': crankiness, clinginess and crying. Alongside these you may see frequent waking, a disrupted sleep pattern, constant demand to feed, reduced appetite and increased wariness of strangers.
Leaps usually last 1-3 weeks and pass on their own. Trying to establish new habits during one — starting sleep training, dropping the dummy — is generally not a good idea; it is far easier once the leap is over.
An important distinction: fever, vomiting, diarrhoea, a rash or weight loss are not symptoms of a leap. If you see those, contact your doctor.
How Do You Get Through a Leap?
Lower your expectations: going with the flow is less exhausting than making plans in these weeks. Meeting your baby's extra need for closeness will not spoil them.
Keep the sleep routine intact. The routine itself gives your baby predictability, and as long as the content stays the same, settling gets easier.
Arrange support for yourself. Leap weeks are more tiring for the parent than for the baby; taking turns and short breaks make the period far more manageable.
Frequently Asked Questions
Are leap weeks calculated from the birth date?
No, they are calculated from the due date. Because leaps depend on brain maturation, being born early or late doesn't shift the calendar. Use the due date rather than the birth date in the calculation.
How long does a leap last?
Usually 1-3 weeks. Leaps in the early months tend to be shorter and later ones longer. The duration varies from baby to baby and it resolves on its own.
What are the symptoms of a leap?
The most typical signs are crankiness, clinginess and wanting to be held constantly. These can come with frequent waking, disrupted sleep, constant demand to feed and reduced appetite. Fever, vomiting or a rash are not leap symptoms — see a doctor in those cases.
How many leap weeks are there?
The commonly used model defines 10 leaps in the first two years: at roughly weeks 5, 8, 12, 19, 26, 37, 46, 55, 64 and 75. These weeks are counted from the due date.
Should you start sleep training during a leap?
Generally not. A baby's need for closeness increases during a leap, and establishing a new routine makes it harder for both of you. Starting once the leap has passed is much easier.
Understand leaps through your own records
Once you log sleep and feeds, leaps stop being guesswork and become data. Log with a single tap in Baby Wallie and see the pattern on a chart. Free for 7 days.
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This content is for informational purposes only and does not replace medical advice. Always consult your doctor or midwife about your own or your baby's health.