San Mateo County property tax deadlines for 2026
The two appeal windows, the bill due dates, and what to do if you're late — all specific to San Mateo County.
San Mateo County has two property tax appeal deadlines, because it has two separate processes. The free informal review with the San Mateo County Assessor-County Clerk-Recorder & Elections: by October 31. The formal appeal with the County of San Mateo Assessment Appeals Board: July 2 – November 30, with a $30 filing fee. Both measure your home's value as of the same date: January 1, the lien date.
Everything on this page is specific to San Mateo County. For how the deadlines work statewide — and why some counties' formal deadline is September 15 while others run to November 30 — see the California-wide deadlines guide. For the full step-by-step appeal process here, see the San Mateo County appeal guide.
The two appeal deadlines in San Mateo County
Free · No hearing
Informal decline-in-value review
- Window
- by October 31
- Form
- Decline in Value Reassessment Application
- Submitted to
- San Mateo County Assessor-County Clerk-Recorder & Elections
- Fee
- Free
- Typical response
- results mailed by July of the following year
A county appraiser reviews your comparable sales evidence. Your value goes down or stays the same — it cannot be raised through this process.
Binding · Preserves appeal rights
Formal assessment appeal
- Window
- July 2 – November 30
- Form
- BOE-305-AH
- Heard by
- County of San Mateo Assessment Appeals Board
- Fee
- $30
San Mateo County recommends filing the formal appeal even while an informal review is pending, so a slow informal answer can't cost you the year.
The San Mateo County property tax year at a glance
| Date | What happens | Why it matters |
|---|---|---|
| Jan 1, 2026 | Lien date | Your home's value for this year's bill is fixed as of this date. All appeal evidence points back here. |
| July 2 – November 30 | Formal appeal window | File BOE-305-AH with the Clerk of the Board. |
| Nov 1 / Dec 10 | First installment | First property tax installment due Nov 1, delinquent after Dec 10. Pay it even if your appeal is pending — you get a refund with interest if you win. |
| Feb 1 / Apr 10 | Second installment | Second installment due Feb 1, delinquent after Apr 10. |
The informal review window (by October 31) runs on the San Mateo County Assessor-County Clerk-Recorder & Elections's schedule — see the cards above. Supplemental and escape assessments have their own clock: generally 60 days from the date printed on the notice.
Not sure the deadline matters for you yet? Start with whether you're overassessed at all — free, about 60 seconds.
Check my propertyWhat if I missed a deadline?
Missed the informal window? If the formal window (July 2 – November 30) is still open, file the formal appeal — same evidence, and your appeal rights are preserved with a binding decision at the end.
Missed both? For a regular decline-in-value case, you wait for the next January 1 lien date and file in next year's windows. The deadlines aren't extendable, but nothing stops you from preparing early — the evidence rules reward sales close to the lien date, so the strongest comps for next year's appeal close between this fall and next March.
Got a supplemental or escape assessment notice? Those carry their own appeal window — generally 60 days from the date on the notice — independent of the windows above.
Who to contact in San Mateo County
San Mateo County Assessor-County Clerk-Recorder & Elections
Informal decline-in-value reviews
- Phone: (650) 363-4500
- Email: assessor@smcacre.gov
- Website: smcacre.gov/
Clerk of the Board — County of San Mateo Assessment Appeals Board
Formal assessment appeals
- Phone: (650) 363-4573
- Email: AAB@smcgov.org
- Mail: County of San Mateo Assessment Appeals Board, 500 County Center, 5th Floor, BOS 104, Redwood City, CA 94063
Common questions
When is the deadline to appeal property taxes in San Mateo County?
There are two separate deadlines. The free informal review with the San Mateo County Assessor-County Clerk-Recorder & Elections: by October 31. The formal appeal with the County of San Mateo Assessment Appeals Board: July 2 – November 30. They are independent processes — if the informal review hasn't come back before the formal window closes, file the formal application as a backstop so you don't lose your appeal rights for the year.
Does it cost anything to appeal in San Mateo County?
The informal decline-in-value review is free. The formal appeal to the County of San Mateo Assessment Appeals Board has a $30 filing fee. In both cases the evidence is the same: recent comparable sales showing your home's market value on January 1 was below your assessed value.
What form do I need for a San Mateo County property tax appeal?
For the informal review, San Mateo County uses the Decline in Value Reassessment Application form, submitted to the San Mateo County Assessor-County Clerk-Recorder & Elections. For the formal appeal, you file BOE-305-AH with the Clerk of the Board during the July 2 – November 30 window.
What if I miss the San Mateo County appeal deadline?
If you miss the informal window but the formal window (July 2 – November 30) is still open, file the formal appeal. If both have closed, you generally have to wait for the next January 1 lien date and file in next year's windows — current-year deadlines aren't extendable for a regular decline-in-value case. Exceptions exist for supplemental and escape assessments, which carry their own clock: generally 60 days from the date on the notice.
Deadlines only matter if you're overassessed.
Enter your San Mateo County address and we'll compare your assessed value to recent comparable sales — free, in about 60 seconds.
Deadlines and fees above are sourced from the county's published materials and reviewed when the county publishes updates — but counties can change dates and fees mid-season. Confirm on the county website before relying on a specific date. Overassessed provides estimates based on publicly available data and AI-generated analysis. This is not a formal appraisal, legal advice, or tax advice. Results are not guaranteed, and appeal outcomes depend on county review.