Supplemental Assessments

Starting in the 1983-84 tax year, property owners became responsible for taxes on any new base assessed value starting from the “event” date of any change in ownership or completion of new construction. Supplemental assessments and taxation laws are covered in California Revenue and Taxation Code sections 75.10 through 75.55. These sections can be found on the Internet at or through the State Board of Equalization Property Taxes Law Guide. The basic provisions are covered in Revenue & Taxation Code sections 75.10 and 75.11.

Supplemental assessments are an adjustment for the difference between the new market base value as determined by the Assessor, and the current fiscal year assessed roll value. For event dates occurring from January through May there may be two supplemental assessments made, one to adjust the current roll year already billed and one for the future roll that is being prepared. The Assessor will issue a valuation notice explaining the adjustment prior to issuance of a tax bill or refund. If you have questions about your valuation, please contact the Assessor’s office. A sample Supplemental Value Notice may be viewed using this link.

Supplemental Tax Bills/Refunds

Supplemental tax bills and refunds are issued directly to the owner . Those owners with impound accounts for taxes may want to contact their lender to see if they will pay the bill. However, lenders do not typically pay supplemental taxes so the owner/taxpayer should plan to pay them.

Supplemental tax bills and refunds are issued throughout the year as assessments are updated. They are created using the same tax rates as regular roll tax bills and are payable in two equal installments. The first installment is due 30 days following mailing of the tax bill and the second installment is due three months later. Supplemental bills are also prorated to reflect the number of months or days remaining after the “event date” in the fiscal year affected. If you have questions regarding issuing of supplemental tax bills or collection of taxes please contact the Treasurer-Tax Collector.

A reduction in value will result in a single supplemental tax refund and a check will be issued by the Auditor-Controller.