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California · County guide

Contra Costa County property tax appeal

A Contra Costa County property tax appeal is filed between July 2 and November 30 (November 30, 2026 this year). The county's page says to mail the completed application with a $40 check to the Assessment Appeals Board at 1025 Escobar St., Martinez.

This season

Next deadline
Nov 30, 2026
Open now
Contra Costa County Assessment Appeals Board

Opens Jul 2, 2026Closes Nov 30, 2026

Source: Letter To Assessors No. 2026/023: County Assessment Appeals Filing Period for 2026 (BOE, June 2, 2026)Last checked

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Filing fee
$40 (check with the application)
How to file
By mail, Martinez
Office address
1025 Escobar Street, 1st Floor, Martinez, CA 94553 · 925-655-2008
Our coverage
Free check available
  • Independent guide — not affiliated with Contra Costa County or any government agency.
Last updated
October 1, 2026
Sources last checked
October 1, 2026
Status
Verified guide

How we verify facts

When and where do I file a Contra Costa County property tax appeal?

Who hears a Contra Costa County appeal?

One stage. We are not affiliated with this office.

Who hears it: Contra Costa County Assessment Appeals Board

Filing: appeal

Open now

Where is the Contra Costa County office?

Contra Costa County Assessment Appeals Board[1]

Assessment Appeals Clerk

Address
1025 Escobar Street, 1st Floor, Martinez, CA 94553
Hours
Monday-Friday 8 a.m.-5 p.m.

Assessor[8]

Contra Costa County Assessor

Address
2530 Arnold Dr, Suite 100, Martinez, CA 94553
Fax
925-313-7488
Hours
Monday-Friday 8:00 a.m.-4:00 p.m. (office and phones)

We are not affiliated with this office. Hours can change, so call before you visit.

Which Contra Costa County filing windows are coming up?

Contra Costa County filing windows
ClosesAreaWho hears itStatus
Nov 30, 2026CountywideContra Costa County Assessment Appeals Board · Official source · Last checked Sep 29, 2026Open now

When were past Contra Costa County deadlines?

Past Contra Costa County filing windows
Tax yearWindowOffice
2025Closed December 1, 2025Contra Costa County Assessment Appeals Board
2024Closed December 2, 2024Contra Costa County Assessment Appeals Board
2023Closed November 30, 2023Contra Costa County Assessment Appeals Board

How do I file a Contra Costa County appeal?

Filing period
July 2 to November 30
Filing fee
$40, mailed as a check with the application
How to file
Mail the completed application and fee to the Assessment Appeals Board, 1025 Escobar St., Martinez

When is the deadline to appeal a property tax assessment in Contra Costa County?

The soonest deadline we list: Contra Costa County, Contra Costa County Assessment Appeals Board — Closes November 30, 2026.

Deadline detailContra Costa County Assessment Appeals Board · Filing period
Contra Costa County's regular appeals must be filed between July 2 and November 30.[1]

Who decides a property tax appeal in Contra Costa County?

The Contra Costa County Assessment Appeals Board's decision is final and not reheard; the owner or the Contra Costa County Assessor may seek review in superior court. Contra Costa County Assessment Appeals Board: In Contra Costa County, assessment disputes are heard by the Assessment Appeals Board, whose members are appointed by the Board of Supervisors; you file an Assessment Appeal Application.

Appeal stepsContra Costa County Assessment Appeals Board
The Contra Costa County Assessment Appeals Board's decision is final and not reheard; the owner or the Contra Costa County Assessor may seek review in superior court.[2]
What the appeal is calledContra Costa County Assessment Appeals Board
In Contra Costa County, assessment disputes are heard by the Assessment Appeals Board, whose members are appointed by the Board of Supervisors; you file an Assessment Appeal Application.[3]

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

Contra Costa County Assessment Appeals Board: Contra Costa County's page says to mail the completed application with the fee to the Assessment Appeals Board, 1025 Escobar St., Martinez. Contra Costa County Assessment Appeals Board: Contra Costa County posts the Assessment Appeal Application, application fee information and its Rules on Assessment Appeals as PDFs.

How to fileContra Costa County Assessment Appeals Board
Contra Costa County's page says to mail the completed application with the fee to the Assessment Appeals Board, 1025 Escobar St., Martinez.[1]
FormsContra Costa County Assessment Appeals Board
Contra Costa County posts the Assessment Appeal Application, application fee information and its Rules on Assessment Appeals as PDFs.[3]
Filing feeContra Costa County Assessment Appeals Board
Contra Costa County's appeal application is mailed with a $40 check.[1]
Filing feeContra Costa County Assessment Appeals Board · Official FAQ
Contra Costa County's FAQ notes a formal assessment appeal carries a $40 application fee.[4]
Who may fileContra Costa County Assessment Appeals Board
On the Contra Costa County application, an agent must be authorized in writing unless the agent is a California attorney or the owner's spouse, child, parent or registered domestic partner.[2]
Informal reviewContra Costa County Assessment Appeals Board
In Contra Costa County you can ask the Assessor for a free informal value review (Prop 8).[5]
HearingsContra Costa County Assessment Appeals Board
Contra Costa County holds appeal hearings on Thursdays at 9:00 a.m. and mails a written notice about 45 days ahead; to move the date, send a written request to the Assessment Appeals Clerk.[4]

Upcoming appeal deadlines in every county we track

What evidence counts in Contra Costa County, and can the value go up?

Can the Contra Costa County appeals board raise my value?

Yes. Based on the evidence, the Contra Costa County Assessment Appeals Board, like every California appeals board, can raise, lower or keep an assessment.

What evidence can I use in Contra Costa County?

Contra Costa County Assessment Appeals Board: Contra Costa County's instructions ask for comparable sales, cost and income data, where relevant, to support the owner's opinion of value. Contra Costa County Assessment Appeals Board · Exchange: Before a Contra Costa County hearing, the owner may ask for an exchange of information with the Assessor; above $100,000 of assessed value the Assessor may start one.

Evidence acceptedContra Costa County Assessment Appeals Board
Contra Costa County's instructions ask for comparable sales, cost and income data, where relevant, to support the owner's opinion of value.[2]
Evidence ruleContra Costa County Assessment Appeals Board · Exchange
Before a Contra Costa County hearing, the owner may ask for an exchange of information with the Assessor; above $100,000 of assessed value the Assessor may start one.[2]

Can my assessment go up if I appeal in Contra Costa County?

Contra Costa County Assessment Appeals Board: Contra Costa County's appeal instructions say the Contra Costa County Assessment Appeals Board can raise, lower or keep the assessment, depending on the hearing evidence.

Can the value go up?Contra Costa County Assessment Appeals Board
Contra Costa County's appeal instructions say the Contra Costa County Assessment Appeals Board can raise, lower or keep the assessment, depending on the hearing evidence.[2]

Which exemptions can lower my bill without an appeal?

A Contra Costa County owner who owns and lives in the home as a principal residence on January 1 can get the $7,000 Homeowners' Exemption, saving about $70 a year.

Homeowner exemption
A Contra Costa County owner who owns and lives in the home as a principal residence on January 1 can get the $7,000 Homeowners' Exemption, saving about $70 a year.[6]

What do Contra Costa County property taxes and assessments look like?

Figures from public records and the Census, each with its source. They describe the county's homes as a group, not the value of any one home.

How much could a lower assessment save on Contra Costa County property taxes?

Tax rate used: 1.151% of assessed value (county average, fiscal 2024-25).

How much could a lower assessment save on Contra Costa County property taxes?
ExampleTax saved
$10,000 less assessed value$115 a year
10% less on a home assessed at $320,430 (the county's 25th percentile)$369 a year
10% less on a home assessed at $553,014 (the county's median)$637 a year
10% less on a home assessed at $850,000 (the county's 75th percentile)$978 a year

These are examples: the tax rate times a lower assessed value. Exemptions, credits, caps and phase-ins can make the real change smaller. This is not a prediction for any home. Rate source: BOE Annual Report 2024-25, Table 14: average tax rate by county (Property Tax Allocations, BOE Open Data Portal).

What do homeowners in Contra Costa County pay in property tax?

The median owner-occupied home in Contra Costa County was worth $866,800, and the median property tax its owners paid was $7,156 a year, according to the Census Bureau's American Community Survey.

Median home value
$866,800
Margin of error ±$6,426.
Median property tax paid per year
$7,156
Margin of error ±$82.
Median tax as a share of median value
0.83%
A ratio of two medians, not a tax rate. Your own bill depends on your assessment and local levies.
Owner-occupied homes
281,819
Margin of error ±2,360.

These are survey estimates of what owners reported about their own homes. They are not assessed values, not tax rates, and not an opinion of what any home is worth.

They cannot tell you whether your own assessment is fair. That takes a comparison with similar homes, which we offer only in counties we have researched.

From the county's assessment and appeal records

Homes in the county's assessment records
343,538
Median assessed value
$553,014
Middle half of assessed values
$320,430 to $850,000

Source: The county's open assessment data, aggregated by us (tax year 2026 final values). Our calculation from public records; not an opinion of any home's value.

How Contra Costa County home assessments are spread

Assessed values of 343,538 homes in the property classes our free check covers (11, 12, 13, 14, 16 and 5 more), tax year 2026 final values. Half are between $320,430 and $850,000; the median is $553,014. The last bar holds everything above it.Source: Assessment records from the county's open data (tax year 2026 final values), retrieved Sep 27, 2026; our calculation.

Median home value: Contra Costa County compared

  1. Contra Costa County$866,800
  2. Typical California county$481,100
  3. Typical US county$185,300

Contra Costa County $866,800; Typical California county $481,100; Typical US county $185,300

Census survey medians for owner-occupied homes. "Typical" is the middle county of the 58 in California and of all US counties.Source: U.S. Census Bureau, American Community Survey 5-year estimates, table B25077.

Median property tax paid: Contra Costa County compared

  1. Contra Costa County$7,156
  2. Typical California county$3,294
  3. Typical US county$1,619

Contra Costa County $7,156 a year; Typical California county $3,294 a year; Typical US county $1,619 a year

Census survey medians for owner-occupied homes. "Typical" is the middle county of the 58 in California and of all US counties.Source: U.S. Census Bureau, American Community Survey 5-year estimates, table B25103.

Median home assessment by map book

  1. Map book 246$2,446,243
  2. Map book 247$2,250,840
  3. Map book 245$1,971,471
  4. Map book 261$1,933,279
  5. Map book 198$1,925,000
  6. Map book 249$1,899,131
  7. Map book 266$1,766,774
  8. Map book 248$1,758,849
  9. Map book 550$240,797
  10. Map book 561$230,395
  11. Map book 544$229,845
  12. Map book 409$219,301
  13. Map book 534$218,804
  14. Map book 538$206,697
  15. Map book 074$205,561
  16. Map book 901$90,354

The 8 highest and 8 lowest of 267.

Median assessed value by map book: highest Map book 246 ($2,446,243), lowest Map book 901 ($90,354).

Median assessed value of homes in the property classes our free check covers (11, 12, 13, 14, 16 and 5 more) for each map book with at least 50 such homes, tax year 2026 final values.Source: Assessment records from the county's open data (tax year 2026 final values), retrieved Sep 27, 2026; our calculation.

Contra Costa County filing windows on a calendar

  1. Contra Costa County Assessment Appeals BoardNov 30, 2026 · Open now

The dashed line marks today.

Contra Costa County Assessment Appeals Board: Nov 30, 2026

Each bar is a filing window from its opening day to its last day. Forecasts show the expected closing range and are not official dates.Source: the official calendars and rules cited in the sources list below.

How often is property reassessed in Contra Costa County?

Contra Costa County's appeal application instructions explain that the base year is the year the property changed ownership or new construction was completed. In Contra Costa County, market value for a decline-in-value review is measured as of January 1, the lien date.

Reassessment cycle
Contra Costa County's appeal application instructions explain that the base year is the year the property changed ownership or new construction was completed.[2]
Valuation date
In Contra Costa County, market value for a decline-in-value review is measured as of January 1, the lien date.[7]
Level of assessmentDecline in value
Contra Costa County's Prop 8 review form cites R&T Code section 51: the Assessor may temporarily lower an assessed value that is above the January 1 market value.[7]

Homes in Contra Costa County

From the Census Bureau's American Community Survey: how old the homes are, what kind they are, what owners say they are worth and the property taxes they pay. These figures describe all homes together, not any one home.

Median year built
1978
All housing units, owned and rented
Single-family houses, detached or attached
76%
of 429,260 housing units
Owned homes with a mortgage or similar loan
71%
of 281,819 owner-occupied homes

Home values reported by owners

  1. Less than $50,0002%
  2. $50,000 to $99,9991%
  3. $100,000 to $199,9991%
  4. $200,000 to $299,9991%
  5. $300,000 to $399,9993%
  6. $400,000 to $499,9996%
  7. $500,000 to $749,99925%
  8. $750,000 to $999,99922%
  9. $1,000,000 to $1,999,99927%
  10. $2,000,000 or more11%

Home values reported by owners in Contra Costa County: Less than $50,000 2%; $50,000 to $99,999 1%; $100,000 to $199,999 1%; $200,000 to $299,999 1%; $300,000 to $399,999 3%; $400,000 to $499,999 6%; $500,000 to $749,999 25%; $750,000 to $999,999 22%; $1,000,000 to $1,999,999 27%; $2,000,000 or more 11%.

Share of owner-occupied homes in each value range. Owners give this value in the survey; it is not the assessed value.Source: U.S. Census Bureau, American Community Survey, 2020–2024 5-year estimates, table B25075.

Property taxes owners pay a year

  1. No real estate taxes3%
  2. Less than $8002%
  3. $800 to $1,4992%
  4. $1,500 to $1,9992%
  5. $2,000 to $2,9997%
  6. $3,000 or more83%

Property taxes owners pay a year in Contra Costa County: No real estate taxes 3%; Less than $800 2%; $800 to $1,499 2%; $1,500 to $1,999 2%; $2,000 to $2,999 7%; $3,000 or more 83%.

Share of owner-occupied homes by the real estate taxes paid in a year, with or without a mortgage.Source: U.S. Census Bureau, American Community Survey, 2020–2024 5-year estimates, table B25102.

Source: U.S. Census Bureau, American Community Survey (2020–2024 5-year estimates, tables B25075, B25102, B25035, B25024 and B25081), retrieved Oct 1, 2026. Survey estimates have a margin of error.

More questions about Contra Costa County property tax appeals

When is the Contra Costa County property tax appeal deadline?

The Contra Costa County Assessment Appeals Board window closes November 30, 2026.[10][11]

Is there a fee to file a property tax appeal in Contra Costa County?

Contra Costa County's appeal application is mailed with a $40 check.[1]

Where do I file an assessment appeal in Contra Costa County?

Contra Costa County's page says to mail the completed application with the fee to the Assessment Appeals Board, 1025 Escobar St., Martinez.[1]

Can my assessed value go up if I appeal in Contra Costa County?

Contra Costa County's appeal instructions say the Contra Costa County Assessment Appeals Board can raise, lower or keep the assessment, depending on the hearing evidence.[2]

What other rules apply in Contra Costa County?

Contra Costa County Assessment Appeals Board: Filing a Contra Costa County appeal does not postpone the tax bill: taxes are still due by the dates on the bill.

Paying the tax while you appealContra Costa County Assessment Appeals Board
Filing a Contra Costa County appeal does not postpone the tax bill: taxes are still due by the dates on the bill.[2]

Which details are not confirmed yet?

We show a fact only after a person has checked it against the official source. These are still being checked. Until then, ask the Contra Costa County Assessment Appeals Board:

  • When a filing counts as on time

Property tax guides for Contra Costa County homeowners

Counties next to Contra Costa County

California property tax appeals: all counties

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Where do these facts come from?

  1. [1]Assessment Appeals - Contra Costa County (Wayback capture 2026-07-16)Official guide or FAQ · last checked Sep 25, 2026
  2. [2]Assessment Appeal Application (BOE-305-AH) with instructions (Contra Costa County, PDF)Official notice, form, calendar or rules · last checked Sep 29, 2026
  3. [3]Assessment Appeals | Contra Costa County, CA Official WebsiteOfficial guide or FAQ · last checked Oct 1, 2026
  4. [4]Assessment Appeals FAQ | Contra Costa CountyOfficial guide or FAQ · last checked Sep 29, 2026
  5. [5]Review Your Value | Contra Costa County, CA Official WebsiteOfficial guide or FAQ · last checked Sep 27, 2026
  6. [6]FAQs • How do I qualify for a Homeowners' Exemption? | Contra Costa CountyOfficial guide or FAQ · last checked Sep 30, 2026
  7. [7]2026-2027 Request for Value Review (Prop 8), Residential/Multi-Family (Contra Costa County Assessor, PDF)Official notice, form, calendar or rules · last checked Sep 29, 2026
  8. [8]Assessor | Contra Costa County, CA Official WebsiteOfficial guide or FAQ · last checked Oct 1, 2026
  9. [9]Maps & Property Information | Contra Costa County, CA Official WebsiteOfficial guide or FAQ · last checked Oct 1, 2026
  10. [10]Letter To Assessors No. 2026/023: County Assessment Appeals Filing Period for 2026 (BOE, June 2, 2026)Official notice, form, calendar or rules · last checked Sep 25, 2026
  11. [11]Publication 30: Residential Property Assessment Appeals (California State Board of Equalization, February 2020)Official guide or FAQ · last checked Sep 25, 2026
  12. [12]Letter To Assessors No. 2025/020: County Assessment Appeals Filing Period for 2025 (BOE, July 7, 2025)Official notice, form, calendar or rules · last checked Oct 1, 2026
  13. [13]Letter To Assessors No. 2024/022: County Assessment Appeals Filing Period for 2024 (BOE, June 25, 2024)Official notice, form, calendar or rules · last checked Oct 1, 2026
  14. [14]Letter To Assessors No. 2023/023: County Assessment Appeals Filing Period for 2023 (BOE, June 22, 2023)Official notice, form, calendar or rules · last checked Oct 1, 2026
  15. 15.County open data: cocc assessmentsRetrieved Sep 27, 2026; aggregated by us for the charts above.
  16. 16.County open data: cocc assessmentsRetrieved Sep 27, 2026; aggregated by us for the charts above.
  17. 17.U.S. Census Bureau, ACS 2020–2024 5-year estimates, table B25077: Median value (dollars), owner-occupied housing units — Contra Costa County, California
  18. 18.U.S. Census Bureau, ACS 2020–2024 5-year estimates, table B25103: Median real estate taxes paid, owner-occupied housing units — Contra Costa County, California
  19. 19.U.S. Census Bureau, ACS 2020–2024 5-year estimates, table B25003: Tenure (owner- and renter-occupied housing units) — Contra Costa County, California

Data credits: Census ACS (public domain) · Census county adjacency (public domain)

Not affiliated with Contra Costa County or any government agency. Not legal advice. Not an appraisal.

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