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Notice of Supplemental Assessment

Supplemental Assessments

Supplemental assessments are value adjustments required by law when a property:

  1. Changes ownership or
  2. Undergoes new construction

Revenue and Taxation Code, Section 75, et seq.

Purchases and Changes in Ownership

  • A supplemental assessment implements a change in taxable value from the prior owner’s taxable value to the current market value when it is acquired. In other words, a one-time supplemental assessment adjusts for the difference between the prior taxable value and the new taxable value.
  • A supplemental assessment can be an increase or decrease in taxable value.
  • Example 1: Market Value is Higher Than the Prior Owner's Taxable Value
    $250,000 Market Value When the Property was Acquired
    -200,000 Prior Owner's Taxable Value
    $ 50,000 One-Time Supplemental Assessment (A tax bill will be issued)
  • Example 2: Market Value is Lower Than the Prior Owner's Assessed Value
    $200,000 Market Value When the Property was Acquired
    -250,000 Prior Owner's Taxable Value
    $-50,000 One-Time Supplemental Refund (A refund check will be issued)

New Construction and Additions

  • A supplemental assessment for new construction is based on the market value of taxable new construction, and is usually an increase to taxable value. Some examples of taxable new construction include room additions, pools, and patio covers. In addition, significant remodeling that changes the utility, size, or effective age of a property may be considered new construction.
  • Generally, normal maintenance and repairs are not taxable and will not increase your taxable value. Examples of normal maintenance and repairs include a new roof, garage door, kitchen cabinets or counters, and bathroom fixtures.

Supplemental Notices

Supplemental notices are mailed by the Assessor if you:

  • Purchased or acquired property
  • Built something new on your property
  • Supplemental notices indicate the change in value from the prior owner’s assessed value or the change in value for any new construction.
  • Depending on the date of change in ownership or completion of new construction, you may receive one or two supplemental bills. Learn how supplemental bills are assessed.

Supplemental Tax Bills

The Tax Collector mails supplemental tax bills.

  • Supplemental tax bills are prorated from the date of the transfer or completion of new construction to the end of the tax year (June 30).
  • If the supplemental assessment is a positive amount, the County Auditor-Controller will calculate and prorate the supplemental property tax from the date the event occurred, through the end of the fiscal year (June 30). The Tax Collector will mail supplemental tax bill(s) within a few weeks.
  • If the supplemental assessment is a negative amount, a refund may be generated for a portion of the taxes that have already been paid. The County Auditor-Controller will review your payment status, and if you are entitled to a refund, a check will be mailed a few weeks after the tax bills are mailed.