Contra Costa Property Assessment Appeals Due November 30

Contra Costa County homeowners have until Monday, November 30, 2026, to request a review of their property's assessed value or file a formal assessment appeal.

For homeowners whose properties may be assessed above their market value, the process could result in lower property taxes. But not every homeowner will qualify, and understanding the difference between an informal review and a formal appeal is important.

The county's 2026–27 property tax bills have already been issued. The first installment becomes delinquent on December 10, 2026. The county allows payment until 5 p.m. in person or midnight electronically that day before a 10% penalty applies.

The November 30 assessment deadline comes first.

Understanding your home's assessed value

California's Proposition 13 generally limits annual increases in a property's assessed base-year value to 2% or the applicable inflation adjustment, whichever is lower, unless certain events such as a change in ownership or new construction trigger reassessment.

That means longtime homeowners may have assessed values substantially below what their properties would sell for today.

Proposition 8 provides another protection.

When a property's market value falls below its adjusted Proposition 13 base-year value, the county assessor must use the lower value for that assessment year.

These reductions are temporary and are reviewed annually.

For the 2026–27 tax year, the relevant comparison is between a property's assessed value and its market value as of January 1, 2026.

A decline in market value after that date, by itself, does not establish eligibility for a reduction for the current assessment year.

Which Contra Costa homeowners should consider a review?

Homeowners who purchased property relatively recently, particularly near a local market peak, may have more reason to examine their assessments.

The same applies to owners whose properties have experienced changes that could affect market value.

However, a countywide or citywide housing statistic cannot determine whether an individual property has been overassessed.

According to the California Association of Realtors, the median sale price of an existing single-family home in Contra Costa County was $870,000 in September 2026, compared with $869,000 in September 2025, an increase of approximately 0.1%.

In Walnut Creek, Redfin reported a median sale price of $847,660 across all home types for the three months ending October 2026, up 3.4% from the comparable period a year earlier.

These figures describe different geographic areas and housing categories. Neither establishes the market value of a particular home on January 1.

A homeowner considering a review should instead examine comparable properties that sold near the relevant valuation date.

For owners who purchased many years ago, the Proposition 13 assessed value may already be substantially below current market value, making a reduction less likely. Individual circumstances can vary.

Two ways to challenge your assessment

Contra Costa County offers two distinct procedures.

1. Request a free informal value review

The Contra Costa County Assessor's Office provides a free Request for Value Review under Proposition 8.

The residential and multifamily form asks homeowners to provide their opinion of the property's market value as of January 1, 2026.

It also provides space for up to three comparable property sales, including sale dates, prices, square footage, and other relevant characteristics.

The county's form specifies that comparable sales must have occurred before March 31, 2026.

Homeowners may also attach additional supporting information.

The completed request must be returned to the Assessor's Office by November 30, 2026.

The form is available through the county's Review Your Value webpage.

The Assessor's Office can be reached at (925) 313-7400.

2. File a formal assessment appeal

Homeowners may also challenge their assessment through the county's Assessment Appeals Board, which operates separately from the Assessor's Office.

Regular assessment appeals must be filed between July 2 and November 30.

The county lists a $40 filing fee for a formal appeal.

The application and instructions are available on the county's Assessment Appeals webpage.

An informal review does not replace a formal appeal.

Submitting a request to the Assessor's Office does not automatically preserve a homeowner's right to a hearing before the Assessment Appeals Board.

Homeowners who want to preserve that right must file a timely Application for Changed Assessment.

Those awaiting an informal review decision should pay particular attention to the November 30 formal appeal deadline rather than assume the review will be completed beforehand.

Different deadlines may apply to certain supplemental or other special assessments.

What evidence should homeowners gather?

A strong request focuses on the value of the individual property rather than broad housing-market trends.

Useful information may include:

• Comparable homes that sold near January 1, 2026.
• Properties with similar square footage, age, condition, and location.
• Differences in lot size, renovations, or other features that affect value.
• Documented property conditions that may reduce market value.

The county's informal review form permits homeowners to identify up to three comparable sales and attach additional supporting materials.

The central question is whether the property's market value on January 1, 2026, was lower than the assessed value used for the tax year.

Do homeowners still have to pay their property taxes?

Yes.

Requesting an informal review or filing a formal appeal does not suspend property tax payment deadlines.

The first installment of Contra Costa County's 2026–27 secured property taxes becomes delinquent on December 10, 2026. The county allows payment until 5 p.m. in person or midnight electronically that day.

A 10% penalty applies to late payments.

If an assessment is subsequently reduced, the county can adjust the taxes and issue an appropriate correction or refund.

Homeowners should not delay payment while waiting for a review or appeal decision.

Is an assessment reduction permanent?

Not necessarily.

A Proposition 8 reduction is temporary. The Assessor's Office reviews the property's market value each year.

If market conditions improve, the assessed value may increase by more than 2% in a year while the property remains under a Proposition 8 reduction.

However, the assessment cannot exceed the property's adjusted Proposition 13 base-year value solely because of that recovery.

The State Board of Equalization also explains that Proposition 8 reviews generally concern the most recent January 1 assessment, not earlier tax years.

What homeowners should do before November 30

Homeowners who suspect their properties are overassessed should compare their assessed values with evidence of market value as of January 1, 2026.

Those who believe a reduction may be warranted can submit the county's free review form.

Anyone seeking the independent hearing process should review the formal appeal requirements and deadline separately.

For most homeowners, the existing assessment may be appropriate. But for those whose properties were worth less than their assessed values on January 1, reviewing the numbers before November 30 could be worthwhile.

Official resources

• Contra Costa County — Review Your Value
• 2026–27 Request for Value Review (PDF)
• Contra Costa County — Assessment Appeals
• Contra Costa County — Secured Property Taxes
• California State Board of Equalization — Proposition 8 FAQs
• California Association of Realtors — September 2026 Housing Report
• Redfin — Walnut Creek Housing Market

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About the author: Greg McDaniel is an East Bay real estate professional with approximately 27 years of industry experience. He is affiliated with McDaniel Real Estate Group at eXp Realty. His views are his own.

Editor's note: This article provides general information about property assessments and should not be considered individualized tax or legal advice.