Burlingame and Hillsborough homeowners who think their property is overvalued can now challenge their assessments online for the first time.

San Mateo County announced Monday, Sept. 21, a new online portal for the Assessment Appeals Board. The system lets property owners file appeals, pay fees, upload documents and track their case status around the clock. The filing window for regular assessment appeals is open.

Until the portal went live, the process was entirely paper-based. Homeowners had to print a state form, sign it in blue ink, write a check and mail or hand-deliver the packet to county offices in Redwood City, according to property tax guide Overassessed.co.

The county said in its announcement that the portal replaces paper forms.

The shift comes as property values in the area keep climbing. Assessor Mark Church reported in July that the county's 2026-27 assessment roll hit a record $357.6 billion, up 4.85% from the prior year. Burlingame ranked fifth among county cities in dollar growth, adding $1.15 billion in assessed value, according to the Assessor's report. The median single-family home sale price countywide reached $1,980,000 in 2025.

6,572 properties qualified for a reduction in assessed value under California's Proposition 8 decline-in-value program for 2026-27, resulting in roughly $3.5 billion in temporary reductions, according to the same report.

The Board of Supervisors approved a contract amendment with IBM on May 19 to enhance the portal, raising the total project cost to $1,856,738.63, according to board records. The resolution cited improvements to "usability and simplifying navigation."

A formal appeal carries a $30 filing fee per parcel, according to Overassessed.co. The county's own announcement did not specify the fee amount.

The county recommends filing a formal appeal even while an informal review with the Assessor's office is pending, so a slow response does not cost a homeowner their appeal rights for the year. In 2023, 97.6% of decided Assessment Appeals Board cases in San Mateo County were resolved through negotiation, meaning most homeowners never appeared at a hearing.

The filing deadline is Nov. 30. Homeowners can access the portal at smcgov.org/aab.