Contra Costa County, CA Property Tax Appeal Deadline 2026

California reassesses most homes only when they change hands (Proposition 13), but the assessed value on your 2026 tax bill can still be too high — especially under Proposition 8, which requires the assessor to use the lower of your factored base-year value or the property's market value as of January 1, 2026. If comparable homes around Concord, Richmond and Walnut Creek sold for less than your assessed value implies, you have a case.

Appeals in Contra Costa County are heard by the Contra Costa County Assessment Appeals Board, an independent body separate from the assessor. You file BOE-305-AH (Application for Changed Assessment) during the regular filing window: July 2 – November 30, 2026. Filing fee: $40 per parcel/application.

• Contra Costa County does not mail assessment notices to every taxpayer, so its regular-period deadline is November 30 — but don't wait: hearings are scheduled in filing order.

How to appeal in Contra Costa County — step by step

1. 1

   Check your assessed value

   Find your 2026 assessed value on the assessor's website or your value notice, and compare it against what similar homes near you actually sold for around January 1, 2026.

2. 2

   Gather comparable sales

   Three to five sales of similar homes (size, age, neighborhood) closed near the January 1 lien date are the core of a residential appeal.

3. 3

   File BOE-305-AH (Application for Changed Assessment)

   Submit to the Contra Costa County Assessment Appeals Board within the window (July 2 – November 30, 2026). Paper filing by mail or in person (no online portal). Fee: $40 per parcel/application.

4. 4

   Keep paying your tax bill

   Filing an appeal does not pause your property tax. Pay on time; if you win, the county refunds the difference with interest.

5. 5

   Present your case

   Many counties offer an exchange with the assessor before a formal hearing. If it proceeds to a hearing, you (or your authorized agent) present the comparable sales to the board.

Frequently asked questions

• When is the deadline to appeal property taxes in Contra Costa County in 2026?

  The regular filing window for a 2026 Contra Costa County assessment appeal runs July 2 through November 30, 2026. For supplemental or escape assessments, you instead have 60 days from the notice date.

• What does it cost to file?

  $40 per parcel/application. If an appeal isn't worth the fee for your situation, a free estimate tells you that before you spend anything.

• Do I need a lawyer to appeal?

  No. Homeowners can file and present their own appeal, or authorize an agent on the BOE-305-AH application itself. The hearing is informal — it's about sales data, not legal argument.

• What if I miss the regular window?

  Supplemental and escape assessments carry their own 60-day appeal window from the notice date. Otherwise you wait for next year's regular window — and a calendar reminder now beats a missed deadline later.