Amends the Property Tax Code. Provides that, for assessment years following the next general assessment after the effective date of the amendatory Act, no increase in assessment may exceed 20% per year. Provides exceptions if: (1) the property is sold, transferred, or conveyed during the taxable year; (2) significant improvements were made to the property; (3) a homestead exemption or other preferential method of assessment was removed with respect to that property during the taxable year; or (4) the increase was due to an equalization factor imposed by the township, county, or Department of Revenue. Effective immediately.