Contra Costa County Property Tax Appeal — California

Rob Hartley·Updated February 16, 2026

Contra Costa County is located in the northern East Bay region of the San Francisco Bay Area with a population of approximately 1.17 million residents as of 2020. The county seat is Martinez, and major population centers include Concord (the largest city), Richmond, Antioch, Walnut Creek, San Ramon, and Pittsburg. Property tax appeals are particularly important in Contra Costa County because the median annual property tax bill of $6,706 is significantly above the national median of $2,400—homeowners pay $4,306 more per year than the typical American. The county's median home value of approximately $548,200 combined with an effective tax rate of 1.17% to 1.36% results in one of the highest property tax burdens in California, ranking the county 72nd highest among all 3,143 U.S. counties.

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

1,165,927

2026 Appeal Deadline: July 2 through November 30, 2026 for regular assessment appeals; within 60 days of notice date for supplemental or escape assessments

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.

Property in Contra Costa County, California — local tax assessment and 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: Spring (typically by mid-April)

In Contra Costa County, California follows Proposition 13 guidelines where properties are assessed at 100% of their market value at the time of purchase or new construction, with annual increases capped at 2% or the inflation rate, whichever is lower. For example: 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 $6,413 in annual taxes at the county's effective rate of 1.17%. However, under Proposition 8, if your property's current market value falls below your assessed value, you can request a temporary reduction to reflect the lower market value.

The Appeal Process

Appeals are heard by the Assessment Appeals Board. Hearings are held on Thursdays at 9:00 a.m. before the Assessment Appeals Board. Both you and an Assessor's representative will present evidence and arguments. The Board, composed of appointed professionals with expertise in property valuation, will make an independent ruling that can increase, decrease, or leave your assessment unchanged based on the evidence presented.

Consider requesting a free informal review first: Contact the Assessor's Office at(925) 313-7400 to request a Proposition 8 value review before filing a formal appeal. This informal process is free, faster, and often resolves disputes without a hearing.

Gather evidence to support your appeal: Collect 3-5 comparable property sales from within 0.5-1 mile of your property, similar in size, age, and condition, with sales dates as close to January 1 (the lien date) as possible. Include photos showing property condition, repair estimates for any damage or deferred maintenance, and an independent appraisal if available.

Complete the BOE-305-AH Application 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.

File your appeal with the $40 fee by the deadline: Submit the completed BOE-305-AH form with a $40 filing fee (check or money order) to the Assessment Appeals Board at 1025 Escobar Street, 1st Floor, Martinez, CA 94553. Regular appeals must be filed between July 2 and November 30; supplemental appeals within 60 days of notice. Keep proof of mailing or delivery.

Receive your hearing notice and prepare your case: You will receive a written notice approximately 45 days before your hearing, scheduled for a Thursday at 9:00 a.m. You must return the notice indicating your intent to appear or your hearing will be automatically cancelled. Organize your evidence including comparable sales, photos, and supporting documents into a clear presentation.

Attend the Assessment Appeals Board hearing: Present your case before the independent Assessment Appeals Board, which is composed of appointed members with expertise in property valuation. Both you and the Assessor's representative will present evidence. The Board will make an independent ruling based on the facts—they can increase, decrease, or leave your assessment unchanged.

Receive the Board's decision: The Board's decision is final and cannot be reconsidered or reheard by the same Board. If your appeal is successful, you will receive a refund of taxes already paid. Continue paying your tax bills on time during the appeal process to avoid penalties.

Appeal to Superior Court if necessary: If you disagree with the Assessment Appeals Board's decision, either you or the Assessor may bring a timely action in Superior Court for judicial review of the Board's determination.

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.

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://contracosta.ca.gov/191/Assessor

Hours: Monday through Friday, 8:00 AM to 4:00 PM

Tax Exemptions in Contra Costa County

Homeowners' Exemption

$7,000 reduction in assessed value (saves approximately $70-80 per year)

Available to property owners who occupy their property as their principal place of residence as of January 1st. This is the most common exemption and provides proof of residency.

Eligibility: Must own and occupy the property as your principal place of residence on January 1st. Applies to single-family homes, condos, mobile homes, multi-unit properties where you occupy one unit, and houseboats.Deadline: February 15 for full exemption; partial exemption available if filed between February 16 and December 10. Once granted, the exemption remains in effect until terminated.

Disabled Veterans' Exemption

Up to $150,000 reduction in assessed value for veterans rated 100% disabled, blind, or paraplegic due to service-connected injury

Provides a significant property tax reduction for qualifying disabled veterans and their unmarried surviving spouses.

Eligibility: Veterans who are 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 veteran.Deadline: Contact Assessor's Office at(925) 313-7470 for application requirements and deadlines

Property Tax Postponement Program (State Program)

Defers current year property taxes; 5% annual interest rate for 2026

State program allowing eligible seniors, blind, or disabled persons to defer current-year property taxes on their primary residence. The state pays the taxes and places a lien on the property.

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 liens.Deadline: 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 age 55+, severely disabled, or victims of wildfire/disaster 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

Official Resources

Contra Costa County Assessor's Office →

Official Assessor's Office website with information on property assessments, exemptions, and value reviews.

Assessment Appeals Board Information →

Official county page with appeal deadlines, filing instructions, and contact information for the Assessment Appeals Board.

BOE-305-AH Assessment Appeal Application Form →

Download the required form to file a formal property tax assessment appeal in Contra Costa County.

California State Board of Equalization - Property Tax Information →

State-level resource for understanding California property tax laws, Proposition 13, exemptions, and appeal procedures.

Check Your Contra Costa County Assessment

Enter your address to see if your Contra Costa County property is overassessed.

✓ All 50 states✓ Instant results✓ $49 flat fee

Frequently Asked Questions

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

For regular assessment appeals in Contra Costa County, you must file between July 2 and November 30, 2026. This window applies to appeals of your annual assessed value as of the January 1, 2026 lien date. If you received a supplemental assessment due to a change in ownership or new construction, you have 60 days from the date printed on the supplemental notice or its postmark date, whichever is later. Similarly, escape assessments and penalty assessments must be appealed within 60 days of the notice date. Missing these deadlines means you forfeit your right to appeal that year's assessment, so it's critical to act quickly once you receive any assessment notice.

How much does it cost to file a property tax appeal in Contra Costa County?

Filing a formal property tax appeal with the Contra Costa County Assessment Appeals Board requires a $40 filing fee, which must be paid at the time you submit your BOE-305-AH application form. The fee can be paid by cash, check, or money order made payable to Contra Costa County Treasurer. However, before filing a formal appeal, you should consider requesting a free informal Proposition 8 review from the Assessor's Office by calling(925) 313-7400. This informal process costs nothing and often resolves assessment disputes without the need for a formal hearing. Many homeowners successfully reduce their assessments through this free review process, saving the $40 filing fee and avoiding the more formal appeal process.

What is the homestead exemption worth in Contra Costa County?

The Homeowners' Exemption in Contra Costa County reduces your property's assessed value by $7,000, which translates to annual tax savings of approximately $70 to $80 depending on your specific tax rate and special assessments. To qualify, you must own and occupy the property as your principal place of residence as of January 1st. The deadline to file for the full exemption is February 15, though a partial exemption is available if you file between February 16 and December 10. Once granted, the exemption automatically renews each year until you no longer qualify or the property changes ownership. New homeowners typically receive an application within 90-120 days after their deed is recorded, or you can contact the Assessor's Office at(925) 313-7481 to request form BOE-266.

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

Contra Costa County does not currently offer an online filing system for property tax appeals. All formal appeals using form BOE-305-AH must be submitted either by mail or in person to the Assessment Appeals Board at 1025 Escobar Street, 1st Floor, Martinez, CA 94553, along with the required $40 filing fee. You can download the BOE-305-AH form from the county's website at https://contracosta.ca.gov, but the completed application with payment must be physically delivered or mailed. However, before filing a formal appeal, you can request a free informal Proposition 8 value review by calling the Assessor's Office at(925) 313-7400, which is often faster and may resolve your dispute without requiring a formal appeal filing.

What happens at an Assessment Appeals Board hearing in Contra Costa County?

Assessment Appeals Board hearings in Contra Costa County are scheduled for Thursdays at 9:00 a.m., and you will receive written notice approximately 45 days before your hearing date. At the hearing, you will present your case to a panel of appointed board members who have professional expertise in property valuation, such as certified public accountants, real estate brokers, attorneys, or certified appraisers. Both you and a representative from the Assessor's Office will present evidence and arguments supporting your respective positions on the property's value. The Board makes an independent decision based solely on the evidence presented, and they have the authority to increase, decrease, or leave your assessment unchanged. You should bring comparable sales data, photographs, repair estimates, and any other documentation that supports your opinion of value as of the January 1 lien date.

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

The amount you can save by appealing your property taxes in Contra Costa County depends on how much your assessed value is reduced and your property's specific tax rate. With the county's effective tax rate ranging from 1.17% to 1.36%, every $10,000 reduction in assessed value saves approximately $117 to $136 in annual property taxes. For example, if you successfully reduce your assessed value from $600,000 to $550,000 (a $50,000 reduction), you would save approximately $585 to $680 per year. These savings continue annually until your property's assessed value is adjusted again. Given that the median annual tax bill in Contra Costa County is $6,706—significantly higher than the national median—even a modest percentage reduction can result in substantial dollar savings, making appeals particularly worthwhile in this high-tax county.

What evidence do I need to win a property tax appeal in Contra Costa County?

To win a property tax appeal in Contra Costa County, you need compelling evidence that your property's market value as of January 1 (the lien date) was lower than the Assessor's valuation. The strongest evidence includes 3-5 comparable sales of similar properties within approximately 0.5 to 1 mile of your home, with similar size, age, and condition, that sold as close to January 1 as possible (generally no more than 90 days after the lien date). Create an adjustment grid that explains any differences between your property and the comparables, such as square footage, lot size, condition, or features. Include clear photographs that document your property's condition, especially any deferred maintenance, damage, or functional issues. Contractor estimates or repair bids for any needed work strengthen your case, as do independent appraisals if available. Organize this evidence into a clear one-page summary stating your opinion of value and why the comparables support a lower assessment than what the Assessor determined.

Can the Assessor increase my property value if I file an appeal in Contra Costa County?

Yes, the Assessment Appeals Board in Contra Costa County has the legal authority to increase, decrease, or leave your assessed value unchanged based on the evidence presented at your hearing. This is explicitly stated in the appeal application instructions and county guidelines. However, increases are relatively rare and typically only occur when the Assessor presents compelling evidence that your property's market value was actually higher than the current assessment. The Board makes its decision based solely on the facts and evidence presented by both you and the Assessor's representative. To minimize the risk of an increase, ensure that you have strong, well-documented evidence supporting a lower value, including recent comparable sales and property condition documentation. If your evidence is weak or you cannot demonstrate that your property was overvalued as of the January 1 lien date, you may want to reconsider filing the appeal.

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 →

More California Counties

Alameda County (Oakland)Butte County (Chico)El Dorado County (Placerville)Fresno County (Fresno)Kern County (Bakersfield)Los Angeles County (Los Angeles)

← All California property tax appeal info

Sources: https://contracosta.ca.gov/2924/Assessment-Appeals | https://contracosta.ca.gov/191/Assessor | https://www.ownwell.com/trends/california/contra-costa-county | https://www.tax-rates.org/california/contra_costa_county_property_tax | https://bhumicalculator.com/countries/united-states/property/contra-costa-property-tax

Last verified: 2026-02-16