A supplemental tax is the result of a reassessment of real property, effective when there is a change in ownership or completion of new construction.
A supplemental assessment is the difference between the assessed value on the roll and the assessed value as of a supplemental event. Not all property is reassessed upon a change in ownership (e.g. business personal property). The county assessor determines whether a change in ownership or new construction has occurred.
Supplemental tax bills are produced throughout the fiscal year and can be either secured or unsecured. Supplemental assessments do not affect the secured lien date bill.
The date of the change of ownership or completion of construction is called the date of event.
The reassessment on the date of event can result in an increase, decrease or no change in taxable value. Usually an increase will produce a bill and a decrease will produce a negative assessment, commonly referred to as a supplemental refund.
A bill or negative assessment refund may be prorated among owners if there is a subsequent change in ownership in the period. There may be a subsequent change in ownership following an initial change in ownership or completion of new construction, prior to the mailing of the initial supplemental tax bill. When this situation occurs, the bill is prorated and a portion of the original supplemental tax bill that is attributable to the initial change in ownership or completion of new construction, becomes an unsecured supplemental tax bill.