Supplemental Property Taxes

General Information

On July 1, 1983, California State law was changed to require the reassessment of property as of the first day of the month following an ownership change or the completion of new construction.

What is meant by new construction is any substantial addition to real property (e.g., adding a new room, pool, or garage) or any substantial alteration which restores a building, room, or other improvement to the equivalent of new (e.g., completely renovating an outdated kitchen).


In most cases, this reassessment results in one or more supplemental tax bills being sent to the property owner in addition to the annual property tax bill.

Most changes in ownership caused by the sale of property result in reassessment. Changes in ownership that do not result in the reappraisal of property include:

  • Interspousal transfers
  • The transfer, sale, or inheritance of property between parents and their children
  • The addition of joint tenants

Furthermore, homeowners over the age of 55 years who sell their principal residence and purchase a replacement dwelling within two years that is of equal or lesser market value and is located in the same county are eligible to transfer the pre-sale assessed value of their original property to the replacement dwelling.

For further information, please contact the assessor's office at 925-313-7400.