Contra Costa County Property Tax Appeal, California

Travis Bunn·Updated July 24, 2026

Contra Costa County is located in the northern portion of the East Bay region of the San Francisco Bay Area and was established as one of California's original 27 counties in 1850. With Martinez as the county seat and major population centers including Concord, Richmond, Antioch, Walnut Creek, and San Ramon, the county is home to approximately 1.17 million residents. Property tax appeals are particularly important here because the median annual property tax bill of $6,706 is significantly above the national median of $2,400, meaning homeowners pay $4,306 more per year than the typical American. With a median home value of approximately $548,200 and an effective property tax rate ranging from 1.17% to 1.36%, Contra Costa County ranks 72nd highest among all 3,143 U.S. counties for property tax burden.

Notable cities: Martinez, Concord, Richmond, Antioch, Walnut Creek, San Ramon, Pittsburg, Pleasant Hill

Median Home

$548,200

Tax Rate

1.17%

Annual Tax

$6,706

Population

1,170,606

On the typical Contra Costa County home, valued near $548,200 at the county’s effective tax rate of 1.17%, an over-assessment of even 10% means you are overpaying year after year until you appeal it. Here is how to find out if yours qualifies.

2026 Appeal Deadline: July 2 through November 30, 2026

That is at most 97 days away. Your exact date is on your assessment notice, so do not wait on it.

Regular assessment appeals for the current tax year must be filed between July 2 and November 30 of each calendar year. For supplemental assessments (resulting from change of ownership or new construction) or escape assessments, you have 60 days from the date printed on the notice or its postmark date, whichever is later. Missing these deadlines means you cannot appeal that year's assessment.

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California residential street with palm trees at sunset. Contra Costa County appeal guide.

How Contra Costa County Assesses Property

100%of market value

Assessed by: Contra Costa County Assessor's Office

Assessment cycle: annual

Notices typically mailed: July-August

In California, properties are assessed at 100% of their market value at the time of purchase or new construction, with annual increases capped at 2% under Proposition 13. If your home's market value is $548,200 (the county median), at California's 100% assessment ratio your assessed value would be $548,200, resulting in approximately $6,414 in annual taxes at the county's effective rate of 1.17%. The assessed value can only increase by a maximum of 2% per year unless there is a change in ownership or new construction, which triggers a reassessment to current market value.

The Appeal Process

Appeals are heard by the Assessment Appeals Board. You will present your evidence to the Assessment Appeals Board at a hearing typically scheduled on a Thursday at 9:00 a.m. The board will review your comparable sales data and supporting documentation, then issue a binding decision on whether to reduce your assessed value.

Step 1: Request an informal review with the Assessor's Office (optional but recommended). Contact the Assessor at (925) 313-7400 for a free informal value review. The Assessor will compare your evidence to their data and may reduce your assessed value without needing a formal hearing.

Step 2: Gather your evidence including 3-5 comparable sales within 0.5-1 mile of your property, similar in size, age, and condition, that sold close to January 1 of the tax year. Include property photographs showing condition issues, repair estimates for deferred maintenance, and an adjustment grid explaining differences between your property and comparables.

Step 3: Complete the BOE-305-AH Application for Changed Assessment form. Obtain the form from the county website or Assessment Appeals Board office. Fill out all required sections including your property information, Assessor's Parcel Number (APN), current assessed value, and your opinion of the correct value. Incomplete applications may be rejected.

Step 4: File your appeal with the $40 fee by the deadline. Submit the completed BOE-305-AH form with a $40 filing fee between July 2 and November 30 for regular assessments, or within 60 days of notice for supplemental assessments. Keep proof of mailing or delivery.

Step 5: Receive your hearing notice and prepare your case. You will receive a written notice approximately 45 days before your hearing, typically scheduled for a Thursday at 9:00 a.m. Organize your evidence packet with comparable sales data, photographs, and supporting documentation.

Step 6: Attend your Assessment Appeals Board hearing. Present your evidence to the board explaining why your property's assessed value exceeds its market value. The board will issue a decision, and if successful, your assessed value will be reduced and you'll receive a refund for any overpaid taxes.

Step 7: If your appeal is denied and you disagree with the Assessment Appeals Board decision, you may file an action in Superior Court within six months after filing a claim for refund with the county. Contact the Contra Costa County Superior Court for filing procedures.

Required form: BOE-305-AH (Application for Changed Assessment)

Filing Methods

mail:Mail completed BOE-305-AH form with $40 filing fee (check or money order payable to Contra Costa County Treasurer) to: Assessment Appeals Board, 1025 Escobar Street, 1st Floor, Martinez, CA 94553

in-person:Deliver application and $40 fee in person to: Assessment Appeals Board, 1025 Escobar Street, 1st Floor, Martinez, CA 94553. Cash, check, or money order accepted. Office hours: Monday through Friday 8:00am to 4:00pm

Evidence to Bring

Comparable property sales (3-5 properties within 0.5-1 mile, similar characteristics, sold near January 1)Property photographs showing condition and any defectsRepair estimates or contractor bids for deferred maintenanceIndependent appraisal report (optional)Adjustment grid explaining differences between your property and comparables

Contra Costa County Assessor Contact

Contra Costa County Assessor's Office

Phone: (925) 313-7400

Address: 2530 Arnold Drive, Suite 100, Martinez, CA 94553

Website: https://www.contracosta.ca.gov/191/Assessor

Hours: Monday through Friday 8:00am to 4:00pm

Tax Exemptions in Contra Costa County

Homeowners' Exemption

$7,000 reduction in assessed value (approximately $70 annual savings)

Reduces the assessed value of your owner-occupied primary residence

Eligibility: Property owners who own and occupy the property as their principal place of residence as of January 1Deadline: February 15 for full exemption; February 16 through December 10 for 80% of exemption

Disabled Veterans' Exemption

Up to $150,000 off the assessed value

Exemption for veterans rated 100% disabled, blind, or paraplegic due to service-connected disability

Eligibility: Veterans rated 100% disabled, blind, or paraplegic due to a service-connected disability incurred while in the armed forces, or the unmarried surviving spouse of such veteranDeadline: File with the Assessor's Office; contact (925) 313-7400 for specific deadlines

Property Tax Postponement Program

Defers payment of property taxes

State program allowing eligible seniors and disabled persons to defer property taxes

Eligibility: Age 62 or older, blind, or disabled; household income of $45,000 or less; at least 40% equity in the home; no reverse mortgage or other tax liensDeadline: December 10, 2026 (file with State Controller's Office, not the county)

Proposition 19 Base Year Value Transfer

Transfers existing low assessed value to new home with adjustments based on value difference

Allows homeowners to transfer their property tax base to a replacement home anywhere in California

Eligibility: Age 55 or older, severely disabled, or victim of wildfire or natural disaster. Can be used up to three times for age/disability (once for disaster)Deadline: Must file within specified timeframe after purchasing replacement property; contact Assessor at (925) 313-7400

Contra Costa County Appeal Packet · $49

Comparable sales evidence, county-specific filing guide, and professional cover letter. Enter your address to get started.

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Frequently Asked Questions

What is the deadline to file a property tax appeal in Contra Costa County for 2026?

The deadline to file a regular assessment appeal in Contra Costa County is between July 2 and November 30, 2026. This filing window applies to appeals of your property's assessed value as of January 1, 2026. For supplemental assessments resulting from a change of ownership or new construction, you have 60 days from the date on the notice or its postmark date, whichever is later. Missing these deadlines means you lose your right to appeal that year's assessment and may continue overpaying property taxes.

How do I file a property tax appeal in Contra Costa County?

To file a property tax appeal in Contra Costa County, complete the BOE-305-AH Application for Changed Assessment form and submit it with a $40 filing fee to the Assessment Appeals Board at 1025 Escobar Street, 1st Floor, Martinez, CA 94553. You can file by mail or in person during office hours (Monday through Friday 8:00am to 4:00pm). The form requires your property information, Assessor's Parcel Number, current assessed value, and your opinion of the correct value. Include supporting evidence such as comparable sales data, property photographs, and repair estimates to strengthen your appeal.

What is the Homeowners' Exemption worth in Contra Costa County?

The Homeowners' Exemption in Contra Costa County reduces your assessed value by $7,000, which results in approximately $70 in annual property tax savings. To qualify, you must own and occupy the property as your principal place of residence as of January 1. You must file Form BOE-266 with the Contra Costa County Assessor by February 15 for the full exemption. If you file between February 16 and December 10, you can still receive 80% of the exemption for that year. Once approved, the exemption automatically renews each year until you sell or change your primary residence.

What evidence do I need for a successful Contra Costa County property tax appeal?

For a successful appeal in Contra Costa County, you need 3-5 comparable property sales within 0.5 to 1 mile of your home that are similar in size, age, and condition, and sold close to January 1 of the tax year. The Assessment Appeals Board wants actual closed sales data, not online estimates from Zillow or Redfin. Additionally, include property photographs showing condition issues or defects, repair estimates or contractor bids for deferred maintenance, and an adjustment grid explaining differences between your property and the comparables. An independent appraisal report is optional but can strengthen your case.

How much can I save by appealing my property taxes in Contra Costa County?

With Contra Costa County's median home value of $548,200 and effective tax rate of 1.17%, even a 10% reduction in your assessed value would save you approximately $641 per year in property taxes. The actual savings depends on how overassessed your property is compared to its true market value. If market conditions have declined since you purchased your home, or if the assessor overlooked property-specific issues like deferred maintenance, location drawbacks, or condition problems, you could achieve significant reductions. A successful appeal reduces your property taxes not just for one year, but establishes a lower base value that limits future annual increases under Proposition 13.

Should I request an informal review before filing a formal appeal in Contra Costa County?

Yes, requesting an informal review with the Contra Costa County Assessor's Office is highly recommended before filing a formal appeal. The Assessor offers free informal value reviews where a county appraiser will compare your evidence to their data and may reduce your assessed value without requiring a formal hearing before the Assessment Appeals Board. Contact the Assessor at (925) 313-7400 to request an informal review by November 30. If the informal review doesn't resolve the issue or you receive no response as the formal deadline approaches, you can still file a formal appeal between July 2 and November 30 to preserve your rights.

What happens at a Contra Costa County Assessment Appeals Board hearing?

At a Contra Costa County Assessment Appeals Board hearing, which is typically scheduled on a Thursday at 9:00 a.m., you will have the opportunity to present your evidence to the board explaining why your property's assessed value exceeds its market value as of January 1. You'll receive written notice approximately 45 days before the hearing. During the hearing, present your comparable sales data, photographs, and supporting documentation in an organized manner. The county assessor may also present their evidence. The board will then issue a legally binding decision on whether to reduce, maintain, or potentially increase your assessed value based on the evidence presented.

Can I appeal my supplemental tax assessment in Contra Costa County?

Yes, you can appeal supplemental tax assessments in Contra Costa County, which result from a change of ownership or new construction that triggers a reassessment. For supplemental assessments, you have 60 days from the date printed on the notice or its postmark date, whichever is later, to file your appeal. Use the same BOE-305-AH form and $40 filing fee, and submit it to the Assessment Appeals Board at 1025 Escobar Street, 1st Floor, Martinez, CA 94553. Supplemental assessments often catch new homeowners by surprise when they arrive months after closing, so watch for these notices and act quickly if you believe the assessment is too high.

Official Resources

Contra Costa County Assessor's Office →

Official assessor website with exemption applications, assessment information, and contact details for property owners.

Contra Costa County Assessment Appeals Board →

Information about filing formal property tax appeals, hearing schedules, and Assessment Appeals Board procedures.

California State Board of Equalization - Property Tax Information →

State resources on California property tax laws, assessment appeals procedures, and property tax forms including BOE-305-AH.

Contra Costa County Property Tax Bills and Payment →

Access current and previous tax bills, payment information, and details about property tax exemptions and assistance programs.

For state-wide appeal information including California's assessment ratio and deadlines, see our California Property Tax Appeal Guide →

Considering professional help with your appeal? Compare pricing, coverage, and pros/cons in our Best Property Tax Appeal Services (2026) or browse side-by-side service comparisons →

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← All California property tax appeal info

Sources: https://www.contracosta.ca.gov/191/Assessor | https://www.contracosta.ca.gov/2924/Assessment-Appeals | https://www.appealdesk.com/appeals/california/contra-costa | https://www.jvmlending.com/blog/contra-costa-county-property-taxes-a-comprehensive-guide/ | https://www.boe.ca.gov/proptaxes/asmappeal.htm

Last verified: 2026-07-24