County filing guide
San Mateo County property tax review and appeal guide
Regular decline-in-value appeals. Supplemental and escape assessments have different deadlines.
Filing options
Current county filing details have not loaded yet.
These steps explain the regular decline-in-value review and appeal process. They do not confirm that filing is open or that a submission method is currently available. Before filing, check the county’s current window, fees, forms, and submission instructions.
Filing instructions
Informal review
Procedural reference — confirm current availability before filing.
Open the Assessor’s Property Tax Relief page and scroll to Decline in Value Application. Complete the online form below that heading.
Start the Assessor’s online Decline in Value Application. Enter your parcel number, property address, purchase date, current assessed value, and your opinion of market value as of January 1, details not loaded.
Explain the facts supporting your value. To add supporting documents, select Choose File, select your file, and choose Upload.
Complete your name, mailing address, daytime phone, and email. Review the information, complete the reCAPTCHA, and select Submit. Keep a copy of what you sent and any confirmation provided.
Respond if an appraiser requests more information. If you already received a letter asking for documents, send them to the email address in that letter.
The informal review does not extend the formal deadline. The county recommends filing a formal appeal if you have not received the informal result before November 10, details not loaded; the regular appeal deadline is details not loaded.
Formal appeal online
Procedural reference — confirm current availability before filing.
Each parcel and roll year needs its own application. The application fee is nonrefundable.
Open the San Mateo Assessment Appeals Board portal and select Sign in / Register. Existing users can sign in with their email and password.
Start with Sign in / Register in the AAB portal. For a new account, choose Register, then Applicant if you are filing for yourself. Enter the requested contact details, select a security question and answer, choose your correspondence preference, and follow the registration prompts.
After signing in, open the new appeal application. For a claim that the annual assessed value exceeds the January 1 market value, use Regular Assessment and Decline in Value.
Complete the applicant and property information, parcel number, roll year, assessed values, and your opinion of value. Review the county’s application instructions before answering the written-findings and refund questions. Provide representative authorization and notices only when applicable. The application says not to attach hearing evidence at this stage.
Review the application, complete the portal’s certification and submission requirements, and pay the details not loaded filing fee online as prompted. Save a copy and any submission or payment confirmation.
Return to the portal to check status and respond to requests. The county sends a notification when the application is processed. For portal or filing questions, contact the AAB Clerk at details not loaded or [email protected].
After you file
Informal review
Keep your request confirmation and correspondence. Confirm current deadlines with the county.
Formal appeal
Keep a copy of your application and filing confirmation. Watch for notices from the Clerk of the Board and follow the county’s instructions for any hearing.
Open my appeal plans →Contacts & sources
Current county contacts and live fact citations will appear when filing details load.
Sources
Informal sources
- Property Tax Relief and live Decline in Value Application — January 1, 2026 valuation, October 31 deadline, form fields, document upload, reCAPTCHA, Submit, and follow-up instructions.
- About Assessment Appeals — recommendation to file a formal appeal if the informal result has not arrived before November 10.
- Checked September 29, 2026. The blank public form was inspected through its Submit button; no information was entered, CAPTCHA completed, or request submitted. A confirmation screen was not reached.
Formal sources
- AAB portal, login, and registration — live entry and applicant-registration fields directly inspected.
- Portal FAQ and About Assessment Appeals — online filing and payment, fee, filing window, separate applications, processing notifications, and status updates.
- 2026 application and instructions, BOE-305-AH revision May 2024, downloaded from Appeal Forms — required information, appeal categories, certification, and no hearing evidence with the initial application.
- Checked September 29, 2026. Steps after sign-in summarize the county’s published application requirements and portal guidance; the account-only screens, certification sequence, checkout, and confirmation were not inspected. No account, appeal, or payment was created.