"Actual age" is your baby's real age, calculated from her birthday; while adjusted age is calculated from her due date. A baby needs a full 40 weeks (give or take a week) to grow and develop, so the adjusted age takes into account the weeks of pregnancy that are missed due to a premature delivery. For example, consider a baby born at 28 weeks who is now 16 weeks old by actual age and 4 weeks by adjusted age. This baby, technically four months from her birthday, is not expected to have met the same developmental milestones as a four-month-old. Instead, this baby will be more on track with a baby who is one month old.