my baby was born 28 days before due date. so should I subtract that from her actual days of birth to reach the milestones.

A. A typical calculation that works is multiplying the number of months by 4.345. So, for example, if your baby is 11 months old, it would mean that they are 4.345 × 11 = 47.795 weeks old or approximately 48 weeks old. This calculation will tell you how old your infant is in weeks.