The notion of corrected (or adjusted) age is used for children born prematurely. The corrected age refers to the age the child would be if born full-term or on the due date. A child is usually considered premature when born before a gestational age of 37 weeks. The corrected age is calculated by subtracting the gestational age from the equivalent term age, ie 40 weeks. This gives the number of weeks of prematurity, which is then subtracted from the chronological age to give the corrected age. Such age correction makes it possible to take into account brain maturation to assess developmental acquisitions. The corrected age is usually used until the child reaches the chronological age of two years, sometimes three. Up to this age, a few weeks can make a huge difference in a child's abilities.