Real Property


Real Property

Real Property Assessment

The Assessor Division compiles a roll of property tax assessments for delivery to the County Controller by July 1 each year. This “Local Assessment Roll” covers more than 237,000 assessments countywide, value in excess of $206 billion.

A copy of the Local Assessment Roll is available at the Assessor Division front counter for public inspection. The Assessor Division also reassesses personal property each year.

Real Property

Real property is fixed property, principally land and buildings. Under Proposition 13, real property is reappraised when a change in ownership occurs or when new construction takes place. Except under special situations, real property assessments may not be increased by more than 2% annually, unless there is a change in ownership or new construction.

Mobile Homes

A mobile home is a structure that is transportable, used with or without a foundation, and designed and equipped to contain no more than two dwelling units. All mobile homes purchased new after June 30, 1980 and those on permanent foundations are subject to property taxes. As with real property, the assessed value of mobile homes may not be increased by more than 2% annually, unless there is a change in ownership or new construction.

Proposition 13

The assessment process in California was substantially modified in 1978 by California Constitution Article XIII A, also known as Proposition 13. Proposition 13 established base year assessment values, limited annual real property assessment increases to no more than 2 percent, and limited property taxes to 1% of a property’s assessed value.

Proposition 13 allows real property to be reappraised if:

  • A change in ownership occurs; or
  • New construction is completed; or
  • New construction is unfinished on January 1st (also known as the “lien date”); or
  • It is part of an annual review of properties having declining value; or
  • It is part of land conservation contract (Williamson Act)

Supplemental Assessments

When the Assessor reappraises real property due to a change in ownership or completion of new construction, the additional assessment is called a “supplemental assessment” and reflects the difference between the current roll value and the new value. The supplemental assessment generates a supplemental tax bill pro-rated for the number of months remaining in the fiscal year, which runs from July 1 through June 30. This assessment is in addition to the regular tax bill or refund.

Some events create two supplemental assessments. Events occurring January through May, known as the “window period,” affect two fiscal years and require two supplemental assessments. This is because the current tax year, which ends June 30, has not yet ended, and the next tax year’s values were set as of January 1, so both rolls are affected.


How We Assess the Value of Your Property

Factored Base Year Value Diagram

Property tax is based on the taxable value of property. Most often this is a property’s factored base year value (FBYV), but when the market value of a property on the January 1 lien date falls below the FBYV, the assessor is obligated to review the property and enroll the lesser of FBYV or market value under Proposition 8.


How Construction Affects Taxable Value

The Assessor is required to reassess new construction such as an addition or new structure. The Assessor will determine the market value (not necessarily the cost) of the construction, and add that value to the existing property assessment.


Request Change of Address

For Secured or Unsecured Property Tax

Download an address change form

Complete the form and return it to the Assessor via mail, fax or email.


Mark Church Assessor-County Clerk-Recorder
555 County Center, 3rd Floor
Redwood City, CA 94063

Fax: 650.599.7435



Decline in Value Assessment

When an economic downturn occurs, it may affect the local real estate market causing housing and commercial values to drop. The law provides property tax relief to property owners if the value of their property falls below its assessed value.

Generally, property is assessed at the lesser of two values:


Notices of Valuation

Notices of Valuation are mailed out whenever there has been a change in ownership, new construction or a decline in market value which may cause a change in assessment. Business personal property is valued annually. 

Check the Notice of Valuation to make sure the information it contains is correct.


Assessment Appeals

When a property owner disagrees with the Assessor on the value on which an assessment is based, he or she should contact the Assessor’s Division within 15 days of receiving the assessment notice. If a reduction in value is proper, the Assessor will adjust the value.

The Assessor also may conclude that a reduction in value is not warranted. The property owner is entitled to appeal that decision to the Assessment Appeals Board. 


Assessor Maps

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The Property Maps portal allows you to download Assessor’s maps or Recorded maps such as subdivision maps and parcel maps online for free.

These same maps are also available at the County Recorder Division and may be printed there for a fee. You may purchase an official copy at the office during regular business hours (Monday through Friday, 8 a.m. to 5 p.m.) at:

555 County Center, 1st Floor
Redwood City, CA 94063

Click to search Property Maps