Amends the Property Tax Extension Limitation Law in the Property Tax Code. Provides that, if a taxing district grants a property tax abatement for a defined period of time measured in levy years, then, for the first levy year after the expiration of the abatement, the district's aggregate extension base shall be the taxing district's last preceding aggregate extension, subject to certain adjustments, plus the amount of the expired abatement for the previous levy year. Effective immediately.