Property Tax Appeals in San Mateo County, California
San Mateo County's Assessment Appeals Board page sets November 30, 2026, as the deadline for a 2026 regular assessment appeal covering decline in value, base year value, or personal property. Each application requires a non-refundable $30.00 filing fee, and separate applications are required for each roll year and each parcel. The county also runs a separate, informal Decline in Assessed Value Program through the Assessor's Office, with an October 31, 2026 enrollment deadline; because that program is not the formal appeal process, the county recommends filing a formal Assessment Appeal by November 30 to protect appeal rights if a decision has not arrived by November 10. FairPath can organize an owner-managed comparison table, condition exhibits, official links, and a filing checklist. It does not file the application, select the owner's opinion of value, pay the fee, negotiate with the Assessor, or appear at the hearing.
Assessment context: Begin with the Assessor-County Clerk-Recorder & Elections parcel record and confirm whether the dispute concerns the January 1, 2026 lien-date value on the regular roll, a supplemental or escape assessment, or a roll correction. San Mateo County spans dense Peninsula cities near San Mateo and Redwood City, tech-industry corridors toward the Bay, coastal communities along Highway 1, and hillside neighborhoods in the Santa Cruz Mountains foothills, all within one of California's higher-cost housing markets. A property a few miles away is not automatically comparable. Neighborhood, lot topography, view, age, and condition should be confirmed against the Assessor's record before relying on them.
Filing process: Request the Assessment Appeal Application from the Assessment Appeals Board, either through the online Assessment Appeals Board Portal or by emailing the AAB Clerk, and confirm the parcel, roll year, and assessment type before completing it. Include the non-refundable $30.00 filing fee with the application, and attach a copy of the Supplemental or Escape Notice if the appeal concerns one of those assessment types. Submit the original, wet-signed application either through the online portal or by mail or hand delivery to the Assessment Appeals Board Clerk, 500 County Center, 5th Floor, Redwood City, CA 94063. After the application is processed, expect a pre-hearing conference notice at least 45 days before the scheduled evidentiary hearing.
Evidence to review: San Mateo County's pre-hearing conference process initiates the exchange of information between the applicant and the Assessor's Office ahead of the evidentiary hearing, where the Assessment Appeals Board considers the evidence presented. Build a comparable-sales table showing sale date, price, parcel, neighborhood, lot size, living area, age, and condition, and prioritize sales close to the January 1, 2026 lien date; California generally excludes comparable sales occurring more than 90 days after that date. Record lot-size, view, and condition differences between the property and each comparable sale.
Current deadline guidance: 2026 regular assessment appeals: July 2 through November 30, 2026. San Mateo County's Assessment Appeals Board page states that the deadline for filing a 2026 regular assessment appeal (decline in value, base year value, or personal property) is November 30, 2026, consistent with the July 2 opening date and California State Board of Equalization's certified county filing-period table. Supplemental, escape, or roll-correction assessments instead must be filed within 60 days of the mailing date on the notice, or its postmark, whichever is later.
San Mateo County's 2026 regular assessment appeal deadline is November 30, matching the extended deadline group rather than the earlier September 15 group used by some counties.
The county operates a separate, informal Decline in Assessed Value Program through the Assessor's Office, with an October 31, 2026 enrollment deadline distinct from the formal appeal deadline.
San Mateo County offers an online Assessment Appeals Board Portal to submit applications, upload evidence, and track appeal status, in addition to mail or hand delivery.
The Assessment Appeals Board Clerk's office is located at 500 County Center, 5th Floor, in Redwood City, and the county notes the full process can take up to two years.
Official filing authority: San Mateo County Assessment Appeals Board Clerk. https://sanmateotax.my.site.com/AAB
Source: County of San Mateo, About Assessment Appeals, https://www.smcgov.org/ceo/about-assessment-appeals. Reviewed 2026-09-22.
Source: County of San Mateo, Assessment Appeals Board Portal, https://sanmateotax.my.site.com/AAB. Reviewed 2026-09-22.
Source: San Mateo County Assessor-County Clerk-Recorder & Elections, Assessor, https://smcacre.gov/assessor. Reviewed 2026-09-22.
Source: California State Board of Equalization, Letter to Assessors 2026/023: 2026 Assessment Appeal Filing Periods, https://boe.ca.gov/proptaxes/pdf/lta26023.pdf. Reviewed 2026-09-22.
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