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Assessor's Office

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1. My property value was reduced under Proposition 8. Now the Assessment has increased. Why?

Proposition 8 provides that your taxable value does not exceed the current market value of the property. Once a value is temporarily reduced under Proposition 8, it is reviewed annually and adjusted, according to the market value. Once the market value exceeds the adjusted base value, it will be restored.

2. What is a Supplemental Assessment?

State law requires the Assessor to reappraise property as of the date of the change-in-ownership or completion of new construction. The Assessor's Office must issue a supplemental assessment which reflects the difference between the prior assessed value and the new assessment. This value is then prorated based on the number of months remaining in the fiscal year ending June 30. This supplemental is in addition to the regular tax bill.

3. What about NEW CONSTRUCTION reappraisals?

Copies of all building permits are sent to the Assessor's Office by the cities and County. If the construction is new (such as a room addition), a reappraisal is required. If the construction is for replacement, repair, or maintenance, a reappraisal may not be required. In appraising new construction, the market value of the addition is determined and added to the value of the existing property. The existing property, however, is not reappraised. As with a change-in-ownership, the owner is notified of the new assessment and can appeal the value.

4. Is property assessed at the price paid?

Not always. Real property is valued at its current market value on the date it changes ownership. In a majority of cases, the sales price equals market value, but not always.

5. Are there special programs available for Senior Citizens?

The property tax reimbursement or postponement programs once available to senior citizens and to persons who are blind, disabled, or who have difficulty paying property taxes have been eliminated.

Property Tax Reimbursement

The Franchise Tax Board's Homeowner Assistance program provided property tax relief to persons who were blind, disabled, or at least 62 years old, and met certain minimum annual income thresholds. However, the state budget deleted funding for this Program that once provided cash reimbursement of a portion of the property taxes that you paid on your home. For more information, call the Franchise Tax Board at 1-800-852-5711.

Property Tax Postponement

The State Controller's Property Tax Postponement program allowed persons who are blind, disabled, or at least 62 years old, and meet certain minimum annual income thresholds to postpone their property taxes. However, the state budget eliminated the Property Tax Postponement Program. For more information, call the State Controller's Office at 1-800-952-5661 or 916-327-5587.

6. Is there a Builder's Exclusion?

Many taxpayers in the construction industry are unaware that under Section 75.12 of the Revenue and Taxation Code they can be legally exempted from payment of supplemental tax bills resulting from the completion of new construction, simply by requesting a "Builder's Exclusion."

Effective January 1, 2006, developers of single-family subdivisions of five lots or more are granted an automatic builder’s exclusion upon recording the subdivision map. To be granted the Builder’s Exclusion on fewer than five single-family lots or on other types of property, you must submit a letter requesting the exclusion prior to or within 30 days of the start of new construction on land development and/or improvements. The parcels for which you are requesting an exclusion must be intended for resale, and for no other purpose than that incidental to resale, such as a model home. In short, this means that builders should submit a request for an exclusion as soon as they buy raw land intended for development.

Recommendations: Apply for the exclusion as soon as the land is purchased. Apply for the whole tract. If builder's exclusion is granted on the parent parcel and the parcel splits there is no need to reapply. Builders should be aware that after the exclusion is granted they are still responsible for payment of supplemental tax bills based upon the purchase of land for development, and for payment of annual secured tax bills based on the value of land and new construction complete or incomplete on January 1 of each year. Builders owning parcels protected by a builder's Exclusion are also cautioned that should they begin using these parcels for a purpose other than resale, such as rentals, they are required to notify the Assessor's Office of this fact within 45 days after such non-resale use begins.

Requests for Builder's Exclusions should be addressed to: Gus S. Kramer, Assessor ASR Division 2530 Arnold Drive, Suite 400 Martinez, CA 94553 For further information call (925)313-7400.

7. I am over 55 and wish to move to a smaller home. Will my taxes go up?

Proposition 60 was passed by the voters in 1986 allowing those 55 and over to transfer the assessed value of their principal residence to a replacement residence in the same county if the value of the new residence is equal to or less than that of the original residence when sold. A claim form must be timely filed with the Assessor's Office to qualify. Contra Costa County does not accept transfers from other counties. For additional information regarding this exclusion, see R and T code 69.5 or contact our office at (925) 313-7400

8. What is the Williamson Act (Ag Preserve)?

The California Land Conservation Act of 1965, commonly referred to as the Williamson Act, is a tax relief measure for owners of land. The act permits a landowner to sign a contract with the County or City guaranteeing that the land will be preserved for a period of at least 10 years. In return for this guarantee, the Assessor annually values land and growing improvements in the Act using a restricted income approach rather than the market value. The owner will get the benefit of being taxed on the lower of the total base year value, current market value, or restricted (AG Preserve) value. Generally, this means the taxes for the farmer are reduced, sometimes greatly. You must apply to the County Planning Department by October 15 to receive Williamson Act benefits for the following tax year if you wish to place your farm property into the AG Preserve. The Assessor's Office may require you to report data pertaining to your agriculture parcels via an annual AG Preserve Questionnaire.

9. When is Real Estate reappraised?

Under State law (Proposition 13), real property is reappraised only when a change-in-ownership occurs, or upon completion of new construction. Except for these two instances, property assessments cannot be increased by more than 2% annually, based on the California Consumer Price Index. The property tax rate is 1% plus any voter approved bonds, fees, or special charges.

When a sale or transfer occurs, the Assessor's Office receives a copy of the deed and determines if a reappraisal is required under State law. If it is required, an appraisal is made to determine the new market value of the property. The owner is then notified of the new assessment and has the right to appeal the value.

The transfer of property between husband and wife does not require a reappraisal for property tax purposes. This includes transfers resulting from divorce or death. In addition, a refinancing will not cause a reappraisal.

10. If I have an addition to my home, will you reappraise the entire property?

No. Only the value of your new addition will be added to your current assessed value.

11. If I do the work myself, will I only be assessed on the cost of the materials?

No. New construction is assessed at the market value added to the property as of the date of completion, or on January 1, if incomplete.

12. Are mobile homes subject to property taxes?

Newly purchased mobile homes, and those on permanent foundations, are subject to property taxes. As with real property, the assessed value of mobile homes cannot be increased by more than 2% annually unless there is a change in-ownership or new construction. Older mobile homes bought before June 30, 1980 generally are not subject to property taxes. They are licensed under the jurisdiction of the State Department of Housing and Community Development.

As a result of recent State legislation, the purchase of a mobile home park by the residents will not cause a reassessment. Property taxes will remain at their current level and be prorated among the spaces.

13. When can I appeal my assessed value?

Under State law, if the January 1 market value of your property falls below the assessed or taxable value as shown on the tax bill issued in the same year (i.e., January 1, 2009 and tax bill fiscal year 2009/10 issued September 2009), the Assessor’s Office is required to lower the assessment. This type of property tax relief generally applies to recently purchased property. Appeals may be filed between July 2 and November 30 for the annual roll. For supplemental events, or escaped assessments, the appeal must be filed within 60 day of the mailing date of the notice. Appeal forms can be obtained and must be filed with the Clerk of the Board. For more information, call (925) 655-2008.

14. What and when is a lien date?

The lien date is the day that the taxes become a debt on the property and/or owners, even though the valuation and tax bills have not yet been computed and mailed. The tax lien date is January 1. (R&T Code 2192)

15. Why are my neighbor's and my tax bills different when the houses are the same?

Proposition 13, passed by the voters in June 1978, established 1975 as the original base year value and requires that the base value of a property be established as of the date of change of ownership, or as of the date of completion of new construction. If you and your neighbor purchased your properties in different years or have different construction dates, your base values reflect different market values.

16. What happens if I don't pay these taxes?

The issue of non-payment of taxes needs to be addressed with the Tax Collector's office. Their phone number is (925) 957-5280 or visit

Tax Collector

17. How do you calculate taxes?

The taxes are calculated by the Auditor-Controller. Property tax rates vary by area. In Contra Costa County the tax rates average approximately 1.1% of the property's taxable value. For instance, if the taxable value is $10,000, the property taxes could be about $110. Contact the Auditor-Controller at(925) 646-2236 or

Auditor-Controller