The beginning of a leap happens during the fussy phase of the leap. How long this fussy phase lasts varies from leap to leap. So the fussy phase does not indicate the duration of the fussy phase, but when it may begin. The thunderbird indicates the time when your baby is most likely to be in a fussy phase. So your baby can enter the fussy phase during the first day, but also on the last day.

Because we use the due date to calculate the leaps, we know when your baby will make a leap with a margin of +/- 2 weeks. Because of this, it is also possible that your baby will enter a leap earlier than our app indicates.