Assessor's Office
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 how supplemental assessments are calculated along with the resulting estimated supplemental taxes. Please note that the Estimator is intended for changes in ownership only and not for situations where assessed value is added due to new construction.
The Supplemental Tax Estimator will provide estimates for all types of properties; however the results are most reliable for single-family residences and condominiums. Sales prices on these types of properties typically reflect the market value of the property. Change in ownership situations without a sales price (inheritance, foreclosure, etc.) will require an estimate of the fair market value of the property. 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.
If you have atypical situations or have additional questions about supplemental assessments, please call the Assessor’s Office at (510) 272-3787.
To use the Supplemental Tax Estimator, please follow these instructions: Enter the purchase date in mm/dd/yyyy format (e.g., 05/15/2007). Enter the purchase price (or fair market value) using numbers only without the $ sign. Then click Next.

Enter a purchase date no earlier than 01/01/2021 and not later than 12/31/2021 and a purchase price (or fair market value).
Purchase Date: (mm/dd/yyyy) Purchase Price: (or fair market value)