///CALIFORNIA · COUNTY GUIDE
The 2026 regular assessment roll / 2026-27 property tax year deadline to appeal a Contra Costa County property tax assessment is November 30, 2026. The filing window runs from July 2, 2026 to November 30, 2026.
Regular Assessment Appeals must be filed between July 2 and November 30 of each calendar year. California statewide guidance states July 2 is the first day to file regular assessment-roll appeals; the period runs to September 15 if the assessor provided value notices by August 1 to all secured-roll real property assessees, and otherwise through November 30. Contra Costa County’s official assessment appeals page states the county regular appeal period is July 2 through November 30.
| 2026 regular assessment roll / 2026-27 property tax year appeal deadline | November 30, 2026 |
|---|---|
| Filing window opens | July 2, 2026 |
| File with | Contra Costa County Assessment Appeals Board / Clerk of the Board, 1025 Escobar Street, 1st Floor, Martinez, CA 94553 |
| Governing jurisdiction | Contra Costa County Assessment Appeals Board |
| After a successful appeal | A Proposition 8 decline-in-value reduction is reviewed every year and holds while the market supports it. |
| Can a board raise the value? | Yes — see below (Cal. Rev. & Tax. Code §1610.8) |
| Deadline source | Assessment Appeals | Contra Costa County, CA Official Website |
| Last verified | August 16, 2026 |
The 2026 regular assessment roll / 2026-27 property tax year deadline is November 30, 2026. The window opens July 2, 2026. Regular Assessment Appeals must be filed between July 2 and November 30 of each calendar year. California statewide guidance states July 2 is the first day to file regular assessment-roll appeals; the period runs to September 15 if the assessor provided value notices by August 1 to all secured-roll real property assessees, and otherwise through November 30. Contra Costa County’s official assessment appeals page states the county regular appeal period is July 2 through November 30.
Appeals are filed with the Contra Costa County Assessment Appeals Board / Clerk of the Board, 1025 Escobar Street, 1st Floor, Martinez, CA 94553. The governing jurisdiction is the Contra Costa County Assessment Appeals Board.
California assessments start from a Proposition 13 base-year value that rises about 2% a year. Proposition 8 requires the assessor to enroll the lower of that factored base value or the property's current market value, so when the market falls below the roll, a decline-in-value appeal applies. Several counties offer an informal review with the assessor first; formal appeals go to the county Assessment Appeals Board, and a Prop 8 reduction is reviewed every year, holding while the market supports it.
It's possible — a California Assessment Appeals Board equalizes the roll by reducing or increasing an assessment (Cal. Rev. & Tax. Code §1610.8), and the Proposition 13 ceiling protects decline-in-value appeals, not base-year disputes. That's why we check for that exposure before filing: we don't file when we see it, and if it surfaces after filing we withdraw.
Enter your address and we'll check Contra Costa County's own records at no cost. If there's no case, we'll tell you that too.
Serving greater Los Angeles.
California property tax appeals. Any estimate is based on county assessment data and public records and is not a guarantee of any outcome. Representation and fee terms are provided in writing before any filing. Deadline information reflects published county materials as of the date shown above — verify with the Contra Costa County Assessment Appeals Board / Clerk of the Board, 1025 Escobar Street, 1st Floor, Martinez, CA 94553 before relying on it.