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Supplemental Tax

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.

Supplemental Revenue and Taxation Code

Supplemental Calculation Example

When to Expect Two Supplemental Bills

If the date of event is on or after January 1 and on or before May 31 two supplemental assessments resulting in bills or refunds will be calculated. The first supplemental assessment reflects the change in value from the date of event to the end of the current fiscal year. The second supplemental assessment reflects the change in value, from the roll being prepared, for the entire fiscal year.  In this case, you may receive two bills, two refunds, or a bill and a refund - depending on how the Assessor's office has reassessed your property for each fiscal year.

Supplemental Billing Conditions

We are only able to generate a supplemental bill/refund if the following conditions have been met:

  • You have received the Notice of Supplemental Assessment
  • Thirty days have lapsed from the date of that notice
  • The Assessor's Office has certified the event for processing

For example: Notice of Supplemental Assessment received December 01, 2020 (sent by Assessor's Office)
February 15, 2021 - Bill has not been received