Contra Costa County property tax due dates and deadlines for 2026
The bill due dates, the two appeal windows, and what to do if you're late — all specific to Contra Costa County.
Contra Costa County has two property tax appeal deadlines, because it has two separate processes. The free informal review with the Contra Costa County Office of the Assessor: by November 30. The formal appeal with the Contra Costa County Assessment Appeals Board: July 2 – November 30, with a $40 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 Contra Costa 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 Contra Costa County appeal guide.
40 days left to file a formal appeal in Contra Costa County
Applications must be filed with the Contra Costa County Assessment Appeals Board by November 30. The filing fee is $40. Miss it and the next opportunity is next year's filing window.
Not sure you have a case? Check your property free — about 60 seconds, and if you're not overassessed we'll tell you so.
The two appeal deadlines in Contra Costa County
Free · No hearing
Informal decline-in-value review
- Window
- by November 30
- Form
- Request for Value Review (Prop 8)
- Submitted to
- Contra Costa County Office of the Assessor
- Fee
- Free
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
- Contra Costa County Assessment Appeals Board
- Fee
- $40
- Decision window
- Up to 2 years from filing date
Contra Costa County recommends filing the formal appeal even while an informal review is pending, so a slow informal answer can't cost you the year.
Deciding whether to file yourself or pay someone to do it? Compare every California appeal option — free DIY, flat-fee, and full-service — or read the Ownwell vs. Overassessed breakdown.
When is the 2026–27 Contra Costa County property tax bill due?
The 2026–27 Contra Costa County secured property tax bill is paid in two halves. The first is due November 1 and is late after 5 p.m. on Thursday, December 10, 2026. The second is due February 1 and is late after 5 p.m. on Monday, April 12, 2027 — the deadline moves to the next business day when the 10th falls on a weekend.
First installment
- Due
- November 1, 2026
- Late after
- 5 p.m., Thursday, December 10, 2026
- If late
- 10% penalty
Second installment
- Due
- February 1, 2027
- Late after
- 5 p.m., Monday, April 12, 2027
- If late
- 10% penalty plus a $10 cost
- Bills go out by November 1. If yours hasn't arrived, you still owe on time — look it up online.
- On time means received or USPS-postmarked by the deadline.
- Pay on time even while you appeal. If you win, the county refunds the difference with interest.
- Look up or pay your bill: Contra Costa County Treasurer-Tax Collector
The value on your bill
Yes — you can still appeal the value on your 2026–27 bill.
Most of your bill is your assessed value times the tax rate, so the assessed value printed on it is the number an appeal can lower. Start with the free informal review: the Contra Costa County Office of the Assessor takes requests until November 30. The formal appeal to the Contra Costa County Assessment Appeals Board stays open until November 30 (a $40 filing fee).
How to file, step by step: the Contra Costa County appeal guide.
Is the assessed value on your bill too high? Find out free, in about 60 seconds.
Check my propertyThe Contra Costa 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, 2026 | First installment | First property tax installment due Nov 1, late after 5 p.m. December 10, 2026. Pay it even if your appeal is pending — you get a refund with interest if you win. |
| Feb 1 – Apr 12, 2027 | Second installment | Second installment due Feb 1, late after 5 p.m. April 12, 2027 (April 10 falls on a weekend, so the deadline moves to the next business day). |
The informal review window (by November 30) runs on the Contra Costa County Office of the Assessor'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 Contra Costa County
Contra Costa County Office of the Assessor
Informal decline-in-value reviews
- Phone: (925) 313-7400
- Website: www.contracosta.ca.gov/191/Assessor
Clerk of the Board — Contra Costa County Assessment Appeals Board
Formal assessment appeals
- Phone: (925) 655-2008
- Mail: Assessment Appeals Board, 1025 Escobar Street, 1st Floor, Martinez, CA 94553
Common questions
When is the Contra Costa County property tax bill due?
The 2026–27 bill comes in two installments. The first is due November 1 and is late after 5 p.m. on Thursday, December 10, 2026; the second is due February 1 and is late after 5 p.m. on Monday, April 12, 2027. A late installment adds a 10% penalty. Pay on time even if you're appealing — if you win, the county refunds the difference with interest.
When will I get my 2026–27 Contra Costa County property tax bill?
By November 1, 2026 — state law has every California county send its secured property tax bills by then. If yours hasn't arrived, you still owe on time, so don't wait for the mail: look it up online with the Contra Costa County Treasurer-Tax Collector.
When is the deadline to appeal property taxes in Contra Costa County?
There are two separate deadlines. The free informal review with the Contra Costa County Office of the Assessor: by November 30. The formal appeal with the Contra Costa County 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 Contra Costa County?
The informal decline-in-value review is free. The formal appeal to the Contra Costa County Assessment Appeals Board has a $40 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 Contra Costa County property tax appeal?
For the informal review, Contra Costa County uses the Request for Value Review (Prop 8) form, submitted to the Contra Costa County Office of the Assessor. 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 Contra Costa 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 Contra Costa 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.