A Wonder Weeks calculator identifies the 10 developmental leaps that babies experience in their first 20 months, predicting fussy periods that often accompany major cognitive growth spurts.

Wonder Weeks Calculator

Find out if your baby is going through a developmental leap. Based on the 10 major mental leaps in the first 20 months.

All 10 Developmental Leaps

Leap 1: Changing Sensations

Awareness of sensory input changes

Week 4.5–5.5

Leap 2: Patterns

Recognizing simple patterns

Week 7.5–8.5

Leap 3: Smooth Transitions

Perceiving smooth transitions in movement and sound

Week 11.5–12.5

Leap 4: Events

Understanding short sequences of events

Week 14.5–19.5

Leap 5: Relationships

Understanding spatial relationships

Week 22.5–26.5

Leap 6: Categories

Categorizing and grouping

Week 33.5–37.5

Leap 7: Sequences

Understanding and performing sequences

Week 41.5–46.5

Leap 8: Programs

Applying programs — flexible problem solving

Week 50.5–54.5

Leap 9: Principles

Understanding principles and values

Week 59.5–64.5

Leap 10: Systems

Understanding systems and adapting to them

Week 71.5–75.5

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