Supplemental Assessments and Notices

Supplemental Assessment are Value Adjustments Required When a Property:

Changes ownership or
Undergoes new construction

Revenue and Taxation Code, Section 75, et seq.

Purchases and Changes in Ownership

A supplemental assessment represents the increase or decrease in taxable value from the previous owner’s Prop. 13 value to the current market value when you acquire it. In other words, the one-time supplemental assessment adjusts for the difference between the old assessed value (roll value) and the new assessed value (the new base year value).
Essentially, a supplemental assessment picks up the added increment of value. For example, a $250,000 market value transfer that occurs in December on a parcel with a current enrolled value of $200,000 would result in a $50,000 supplemental assessment.
Example 1: Market Value is Higher Than Previous Owner's Prop. 13 Value

$250,000 Market Value When You Acquired the Property
-200,000 Previous Owner's Prop. 13 Value
$ 50,000 One-Time Supplemental Assessment (A tax bill will be issued)

Example 2: Market Value is Lower Than Previous Owner's Prop. 13 Value

$200,000 Market Value When You Acquired the Property
-250,000 Previous Owner's Prop. 13 Value
$-50,000 One-Time Supplemental Refund (A refund check will be issued)

New Construction and Additions

A supplemental assessment for new construction is the market value of taxable new construction and usually increases your taxable value. Examples of new construction include room additions, pools, and patio covers. In addition, the significant remodeling that changes the utility, size, or effective age of a property may be considered new construction.
Normal maintenance and repairs 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 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 previous owner’s Prop. 13 value or the taxable value of the improvement before construction was completed.
Depending on the date of change in ownership or completion of new construction, you may receive one or two supplemental bills. See More Info below for further explanation.

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) in a few weeks.
If the supplemental assessment is a negative amount, a refund may be generated for a portion of the taxes that have 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.