To calculate your baby’s leaps, you must use the due date based on the 40 weeks, and not the date of birth. This may seem illogical, but to calculate when your baby will make a leap, the date of birth is totally irrelevant, only the due date is going to help with this.
The leaps are based on brain development with a margin of maximum 2 weeks. And this starts for all babies at the same time, the moment of conception.
And while the period between conception and the date of birth may be different for all babies, the period between conception and the due date is always the same. So by using the due date, it doesn’t matter if your baby was born too early or too late, because brain development happens at the same rate, inside or outside the womb. Watch this video about the due date.