Think your property assessment is too high? San Mateo County now lets you appeal online
San Mateo County, California – For San Mateo County property owners who think the number on their assessment is simply too high, challenging it no longer starts with a printer, an envelope and a trip to the mailbox.
The county has moved much of the process online, launching a new Assessment Appeals Board portal where taxpayers can file a formal appeal, pay the required fee, sign documents electronically and follow their case at any hour. The timing matters: the regular 2026 appeal window closes Monday, Nov. 30, and county officials say there are no extensions.
San Mateo County announced the new system Sept. 21, describing the goal as making appeals “simpler and more convenient.” The secure portal allows applicants to submit cases online, upload supporting records, receive electronic notifications and monitor their status 24/7.
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Property owners can begin at smcgov.org/aab. Applicants create an account, enter their parcel and assessment information, upload documents, provide an electronic signature and pay a $30 non-refundable filing fee by card. A separate application and fee are required for every parcel and each roll year.
Traditional paper filing remains available. Owners can submit a wet-signed original with a $30 check payable to San Mateo County AAB by mail or in person at 500 County Center, 5th Floor, BOS 104, Redwood City, CA 94063.
The Nov. 30 deadline covers regular 2026 appeals involving decline-in-value claims, base-year values and personal property assessments.
There is also a separate, free “Decline in Value” review offered by the Assessor-County Clerk-Recorder. That informal process has an earlier deadline of Oct. 31. County guidance says property owners who have not received a decision from the Assessor by Nov. 10 should still file a formal Assessment Appeals Board case before Nov. 30 to preserve their appeal rights. If the Assessor later lowers the value, the formal appeal can be withdrawn.
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The Assessment Appeals Board is independent from the Assessor’s office. Its three private-citizen members, appointed by the Board of Supervisors, can lower or confirm an assessment and, in rare circumstances, increase it based on evidence presented during the case.
Hearings and pre-hearings are now conducted in person at the Board of Supervisors’ Chambers at 500 County Center in Redwood City. Because of case volume, the process can take up to two years, although many disputes are resolved during pre-hearing.
Supplemental, escape and roll-correction appeals follow different deadlines and generally must be filed within 60 days of the mailing date or postmark on the notice, whichever is later.
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Questions can be directed to the Assessment Appeals Board clerk at (650) 363-4573 or [email protected]. For owners who believe their Jan. 1, 2026 assessed value is wrong, the county’s message is straightforward: property tax appeals just got easier, but the deadline has not moved.
