Supplemental Assessment Law and Legal Definition

Supplemental Assessment is the determination of tax liabilities at the discretion of the tax authorities.

The supplemental roll provides a mechanism for placing property subject to reappraisals due to change in ownership or completed new construction into immediate effect. Changes in ownership or completed new construction are referred to as ‘supplemental events’ and result in supplemental tax bills that are in addition to the annual property tax bill.

Supplemental assessments apply to real property (land, improvements, and fixtures and taxable possessory interests) but do not apply to personal property or any property not subject to Article XIII A (Proposition 13).