UIC §1275: (a) Unemployment compensation benefit award computations shall be based on wages paid in the base period.

(a) Unemployment compensation benefit award computations shall be based on wages paid in the base period. “Base period” means: for benefit years beginning in October, November, or December, the four calendar quarters ended in the next preceding month of June; for benefit years beginning in January, February, or March, the four calendar quarters ended in the next preceding month of September; for benefit years beginning in April, May, or June, the four calendar quarters ended in the next preceding month of December; for benefit years beginning in July, August, or September, the four calendar quarters ended with the next preceding month of March. Wages used in the determination of benefits payable to an individual during any benefit year may not be used in determining that individual’s benefits in any subsequent benefit year. (b) For any new claim filed on or after April 2, 2012, or earlier if the department implements the technical changes necessary to establish claims under the alternate base period, as specified in subdivision (c), if an individual cannot establish a claim under subdivision (a), then “base period” means: for benefit years beginning in October, November, or December, the four calendar quarters ended in the next preceding month of September; for benefit years beginning in January, February, or March, the four calendar quarters ended in the next preceding month of December; for benefit years beginning in April, May, or June, the four calendar quarters ended in the next preceding month of March; for benefit years beginning in July, August, or September, the four calendar quarters ended in the next preceding month of June. As provided in Section 1280, the quarter with the highest wages shall be used to determine the individual’s weekly benefit amount. Wages used in the determination of benefits payable to an individual during any benefit year may not be used in determining that individual’s benefits in any subsequent benefit year. (c) The department shall implement the technical changes necessary to establish claims under the alternate base period specified in subdivision (b) as soon as possible, but no later than April 2, 2012.