Why the boundary is argued about
One school changes your personal year on 1 January; another changes it on your birthday, and a third blends the two across the months in between. This page uses the calendar year, which is why the result says so on its face. If you were born late in the year and the description feels like it belongs to the year you have just left, the birthday convention is probably the one that fits you — run the calculation again using the previous year and compare.
