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Frequently Asked Questions

This page is for General Questions and they are listed below. FAQs for specific sections are on their own page, and those links are provided below as well.


Business Property Statement Questions

Homeowners’ Exemption Questions

Boat/Watercraft Property Tax Questions


General Questions



Q. What is a Notice of Supplemental Assessment?


A. Under the provisions of Proposition 13, property must be reassessed at market value whenever there is a change in ownership or new construction is completed. A new Base Year Value is established and a supplemental assessment is created.

The new base year value must be the Fair Market Value of the property on the date of the change. If a property has sold, and the purchase price is the same as the market value, then the reported purchase price is enrolled as the new base year value. But if the purchase price is significantly higher or lower than the Market Value of the property on the change date, the assessor is required by law to enroll the Market Value. Market Value is determined by doing an appraisal.

A supplemental assessment is the difference between the new base year value and the value on the assessor’s records for the affected tax year or years. Changes that occur between January and May will create two supplemental assessments; changes occurring between June and December will create one supplemental assessment. The regular tax bill will not be changed or re-issued.

Supplemental assessments are effective the first day of the month following the month in which the change occurs. Supplemental assessments that happen because of an increase in assessed value result in supplemental property tax bills. Supplemental assessments that happen because of a decrease in assessed value result in supplemental refunds being issued. The amount of the supplemental bill or refund is calculated by multiplying the tax rate times the supplemental assessment. Both supplemental bills and supplemental refunds are then pro-rated to cover only the time during the tax year that someone owns a property. Multiple activities during a tax year will result in multiple supplemental assessments; each bill or refund will be pro-rated to cover an assessee’s period of ownership.

The supplemental roll is completely separate from the regular roll. The regular roll is prepared once a year. It is effective January 1st and is delivered to the Auditor’s Office each year on July 1st. The supplemental roll is created throughout the year as changes are processed, and it is delivered periodically through the year.

Supplemental bills or refunds are always mailed directly to the property owner.




Assessor's Office

44 North San Joaquin Street
Second Floor Suite 230
Stockton, CA 95202
Phone: (209) 468-2630
Fax: (209) 468-8383
Office Hours: 8:30 - 4: 30