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    Supplemental Assessments

Supplemental Notices


In addition to annual taxes, you may be responsible for paying supplemental property taxes. State law requires the Assessor to reappraise property upon a change in ownership or new construction. The supplemental assessment reflects the difference between the new assessed value and the old or prior assessed value.

Supplemental Assessments

On July 1, 1983, Senate Bill 813 amended the state Revenue and Taxation Code to create what are known as "Supplemental Assessments." This new law changed the manner in which changes in assessed value were billed by requiring that any increase or decrease in taxes due to a change in ownership or completed new construction became effective as of the first day of the month following the date of change in ownership or the date new construction was completed rather than on the next annual tax bill.

Supplemental assessments result in tax bills that are "in addition to" (that is, supplemental to) the annual property tax bill sent to property owners in October. 

Supplemental Events

Changes in ownership or completed new construction that trigger supplemental assessments are referred to as "supplemental events."

A supplemental event results in a reassessment. A reassessment may be an assessed value increase resulting in a supplemental bill(s), an assessed value decrease resulting in a supplemental refund(s) or retaining the same assessed value (no change). To simplify this guide, we will refer to the supplemental assessment process as though it results in a supplemental bill.

Supplemental Notices

The Assessor determines the fair market value of that portion newly constructed or changed ownership based on the event date.

Once the new assessed value of your property has been determined, the Assessor will send you a Notice of Supplemental Assessment that will show the new assessed value as well as the net supplemental assessment amount.

More about how Property Values Are Assessed

Appealing Supplemental Assessments

Appeals of supplemental assessments must be filed with the Assessment Appeals Board (not the Assessor) within sixty (60) days of the mailing date or the postmark date on the notice of supplemental assessment, whichever is later.

If you feel a supplemental assessment is incorrect, we recommend that you discuss the assessment with the Assessor as soon as possible after receiving your "Notice of Supplemental Assessment" and prior to filing an appeal. Filing deadlines are firm, so please contact the Clerk of the Assessment Appeals Board regarding filing requirements and deadlines.

Important: Filing an appeal does not relieve the applicant from the obligation to pay the taxes on the subject property on or before the applicable due date shown on the tax bill.

More about Assessment Appeals

Depending on the date of the supplemental event, either one or two supplemental tax bills will be produced. Supplemental events that occur between January 1 and May 31 will generate two supplemental bills. Supplemental events that occur between June 1 and December 31 will generate one supplemental bill.

You may also receive more than one supplemental tax bill if more than one supplemental event has occurred in a fiscal year. If this occurs the bills are pro-rated between each owner for the period of time the property was owned

More about Supplemental Taxes

Multiple Supplemental Tax Bills

There are three reasons why an owner may receive more than one supplemental tax bill:

The Supplemental Event Occurred between January 1 and May 31
A supplemental assessment is always generated for the fiscal year in which the event occurred.
An event occurring between January 1 and May 31 will generate a second supplemental assessment for the subsequent fiscal year affected.
The second bill is generated because the annual roll assessment created for the coming fiscal year does not reflect the change in value generated by that event, but must also to be adjusted to reflect the difference as well.
Prior Owner Had a Supplemental Event in the Same Fiscal Year
You can also receive multiple supplemental bills in situations where a series of supplemental events take place within the same fiscal year for different owners. If the bill for the prior owner’s supplemental event is for the same fiscal year in which you took ownership, you will receive a pro-rated portion of that bill for the time period you owned it.
Multiple Supplemental Events Occurred While You Owned the Property
If multiple supplemental events (changes in ownership and new construction) occurred while you own the property, you will receive one or two supplemental bills for each of these events. Supplemental assessments are generated for each assessment.

Read more about Supplemental Taxes


Deva Marie Proto

County Clerk-Recorder-Assessor-Registrar of Voters

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Santa Rosa, CA 95403
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