When real property is purchased, a supplemental assessment is imposed from the date of purchase pro-rated through the current tax year. The Supplemental Tax Estimator provides an estimate of supplemental taxes, along with an estimate of property tax liability for the following tax year. This Supplemental Tax Estimator is intended for changes in ownership only and not for situations where assessed value is added due to new construction.

Note: Values from the Supplemental Tax Estimator, are only estimates and may differ from actual values. Actual values can only be obtained from the County Assessor's office.

While the estimator can provide estimates for all types of properties, transactions involving above or below market value sales prices will influence the accuracy. The accuracy of the supplemental tax estimate will be dependent on the relationship of the purchase price to fair market value.

There are a number of situations in which the Supplemental Tax Estimator will not be able to produce a reliable estimate. The most common are:

  • More than one change in ownership has occurred in a calendar year.
  • Assessed value is added due to new construction.
  • A change in ownership and assessable new construction has occurred in a calendar year.
  • Partial interest transfers where less than 100% of the property has changed ownership.
  • Some new housing tracts or condominium subdivisions in which the map recording and change in ownership has occurred in the same calendar year.

This Supplemental Tax Tool provides only an estimate of potential supplemental tax liability to assist the taxpayer in planning for his/her supplemental taxes. The estimated supplemental tax shown herein is not a substitute for the supplemental bill and may not be relied upon as such.. Please contact your local Assessor’s Office for more information on supplemental assessments, and exact figures for your property.

For further information on Supplemental Assessments, visit the California Board of Equalization's FAQ page at https://www.boe.ca.gov/proptaxes/faqs/suppassessment.htm.

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