County filing guide
How to appeal your property tax in Contra Costa County
Regular decline-in-value appeals. Supplemental and escape assessments have different deadlines.
Filing options
Filing instructions
Informal review
Open the Residential/Multi-Family Request for Value Review form.
Contra Costa informal review — step 1 Enter your contact details, property address, parcel number, and opinion of market value as of January 1, 2026.
Add supporting comparable sales: address or parcel number, sale date, price, square footage, and a description. The form requests sales before March 31, 2026.
Contra Costa informal review — step 3 Sign and date the form, keep a copy, and return it by November 30, 2026 to the Assessor’s Office, 2530 Arnold Drive, Suite 100, Martinez, CA 94553-4359. Questions: 925-313-7400.
Formal by mail
Open the county’s assessment appeals page and download the Assessment Appeal Application. Print the application and read its instructions.
Complete the applicant and property details, including the parcel number from your assessment notice or tax bill. Enter the value on the roll and your opinion of value; leave the Board-only columns blank.
Contra Costa assessment appeal application: applicant, property, and valuation fields. Complete the assessment type, appeal reason, and remaining questions. For an annual January 1 value dispute, use the regular-assessment and decline-in-value selections. Follow the form’s instructions for the refund-claim and written-findings questions.
Sign the application in blue ink. Enclose a $40 nonrefundable check payable to Contra Costa County Treasurer. Do not attach hearing evidence to the initial application.
Keep a copy and mail the signed application and check to Assessment Appeals Board, 1025 Escobar Street, 1st Floor, Martinez, CA 94553, before the regular filing deadline of November 30, 2026. For filing questions, call 925-655-2008.
After you file
Informal review
Keep your request confirmation and any correspondence from the Assessor. Check the formal appeal deadline above when considering a separate appeal.
Formal appeal
Keep a copy of your application and filing confirmation. Watch for notices from the Clerk of the Board and follow the county’s instructions for any hearing.
Open my appeal plans →Contacts & sources
Clerk of the Board
Runs the formal appeal
925-655-2008 · appeals page ↗
1025 Escobar Street, 1st Floor, Martinez, CA 94553
This guide covers the regular decline-in-value appeal; supplemental or escape assessment notices follow different deadlines. Every date and fee here was checked against official sources, listed below with the date checked. If the county's page ever differs from this guide, follow the county's page.
Sources
Informal sources
- Assessor’s forms page and 2026–27 Request for Value Review: current form, required information, deadline, and Assessor’s address.
- Scope: public sources checked September 29, 2026. Existing screenshots retained; no request was submitted.
Informal review
- https://www.contracosta.ca.gov/6919/Review-Your-Value · “Request a FREE Informal Value Review from the Assessor's Office” (checked July 11, 2026)
- https://www.contracosta.ca.gov/DocumentCenter/View/73457/Request-for-Value-Review-Proposition-8-ResMulti · “If you have evidence that the market value of your property as of January 1, 2026 is less than the assessed value, please provide the information below and return this request to the Assessor's Office by November 30, 2026.” (checked September 7, 2026)
Formal sources
- County assessment appeals page: confirms mail filing, fee, mailing address, contact number, and July 2–November 30 regular filing window.
- Assessment Appeal Application and instructions: BOE-305-AH revision 12 (05-24), despite “2020” in the URL; source for application fields, signature, payment, and evidence instructions.
- Scope: public sources checked September 29, 2026. Mail filing is documented; an online filing portal and in-person filing were not verified. This does not establish that mail is the only accepted method. Existing application screenshot retained; no appeal was submitted.
Formal appeal window
- https://www.boe.ca.gov/proptaxes/pdf/lta26023.pdf · “The regular appeals filing period in each county will begin on July 2, 2026, and will end on September 15, 2026, for those counties where the Assessor mails assessment notices to all taxpayers with property on the secured roll by August 1, 2026. For counties where assessment notices are not mailed by August 1, 2026, the filing period is extended to November 30, 2026.” (checked July 10, 2026)
Filing fee
- https://www.contracosta.ca.gov/DocumentCenter/View/68174/Assessment-Appeals-Application-Form-2020 · “A NON-REFUNDABLE FEE OF $40.00 FOR EACH APPLICATION MUST BE INCLUDED AT THE TIME OF FILING THE APPLICATION. Payment can be made by cash, check, or money order payable to Contra Costa County Treasurer.” (checked July 11, 2026)
- https://www.contracosta.ca.gov/DocumentCenter/View/83778/Fee-Schedule · “$40. The $40 fee is charged for each application filed. A separate application is required for each parcel and for each tax year.” (checked July 11, 2026)
Filing address
- https://www.contracosta.ca.gov/2924/Assessment-Appeals · “Once completed, mail application and $40 check to: Assessment Appeals Board 1025 Escobar Street 1st Floor Martinez, CA 94553” (checked July 11, 2026)
Filing channels
- https://www.contracosta.ca.gov/2924/Assessment-Appeals · “Once completed, mail application and $40 check to: Assessment Appeals Board 1025 Escobar Street 1st Floor Martinez, CA 94553” (checked July 11, 2026)
Common questions about appealing in Contra Costa County
When is the deadline to appeal in Contra Costa County?
The deadline to file a formal appeal in Contra Costa County for the 2026-27 tax year is November 30, 2026. Filing opened July 2, 2026.
The Assessor takes informal review requests until November 30, 2026.
What does it cost to file an appeal in Contra Costa County?
The county filing fee for a formal appeal is $40.
There is no fee for the Assessor's informal review.
Informal review or formal appeal: which one first?
Contra Costa County offers both: an informal review with the Assessor, and a formal appeal filed with the Clerk of the Board (due November 30, 2026).
The state's own guidance says to talk to the Assessor's office first: if their staff finds an error, they can lower the roll directly and you may never need to file. Missing an informal review costs you nothing; missing the formal deadline costs you the year.
Which form do I file, and where?
The formal appeal uses the state's application form, BOE-305-AH ↗.
Contra Costa County accepts the formal appeal by mail.
Mail it to the Clerk of the Board at 1025 Escobar Street, 1st Floor, Martinez, CA 94553.
Check the Clerk of the Board's appeals page ↗ or call 925-655-2008 before you file.
How long does an appeal take?
You get written notice at least 45 days ahead, hearings are open to the public (you can watch one first), and boards are expected to decide within two years of filing. You can still settle at any point before your date.
Do homeowners actually get their assessments lowered?
12,906 homes in Contra Costa County had temporarily reduced assessments in tax year 2025-26.