Property Tax Due Dates for Contra Costa County, CA

Property taxes in Contra Costa County are billed in two installments each fiscal year. The first installment is due November 1 and becomes delinquent after 5 p.m. on December 10; the second is due February 1 and becomes delinquent after 5 p.m. on April 10.¹² Miss either cutoff and a 10% penalty attaches automatically. These are the Contra Costa County property tax due dates every owner needs to know.

The Two Installments and Their Delinquency Dates

The county’s tax year runs July 1 through June 30, not the calendar year.³ Your annual bill arrives in the fall and covers that full fiscal year, split into two payments:

First installment: due November 1, delinquent after 5 p.m. on December 10.
Second installment: due February 1, delinquent after 5 p.m. on April 10.

You can pay both at once as soon as the bill arrives, or pay each installment separately before its own delinquency date. There is no early-payment discount, and there is no option to defer without penalty.

When December 10 or April 10 falls on a Saturday, Sunday, or legal holiday, the deadline shifts to 5 p.m. on the next business day.⁴ Check a calendar before assuming you have until the 10th.

For mailed checks, the U.S. Postal Service postmark controls. A payment postmarked on or before the delinquency date is on time even if the county receives it later. Private metered postage does not qualify. Online and phone payments are credited as of the date you complete the transaction through the county’s authorized site, provided you get a confirmation number.⁵ Save that confirmation.

Penalties If You Miss the Deadline

The 10% penalty is automatic. The Tax Collector has no authority to waive it because you forgot, were out of town, or never received a bill. On a $4,000 installment, that is $400. If both installments go delinquent, the second one adds a 10% penalty plus an additional cost.²

Not receiving a bill does not excuse a late payment. The county holds you responsible either way.⁶ If yours hasn’t arrived by late October, call the Tax Collector at (925) 608-9500 or pull a copy from the online portal.

If the taxes are still unpaid when the fiscal year ends on June 30, the property is declared tax-defaulted. A redemption penalty of 1.5% per month then begins accruing on the unpaid amount, which works out to 18% per year on top of what you already owe.⁷ After five years in default, the county can sell the property at public auction to recover what’s owed. For nonresidential commercial property the timeline is three years.⁸

Supplemental Bills Have Their Own Due Dates

If you recently bought a home or finished construction that changed your assessed value, you will get a supplemental tax bill on top of the regular annual bill. Supplemental bills do not follow the November 1 and February 1 schedule. Their due dates depend on when the bill is mailed and are printed on the bill itself.⁶

Supplemental bills are not sent to your mortgage company and are not paid from escrow. You pay them personally, by the deadlines on the bill, and the same 10% penalty applies if you miss them.⁶

If Your Lender Pays Through Escrow

When a mortgage lender pays your property taxes from an impound account, the county still mails you a copy of the bill stamped “INFORMATION COPY” in the upper-right corner.⁶ That is a notice, not a receipt. Confirm with your lender before each delinquency date that the payment actually went through.

After a refinance, the new lender may not have the bill, and the old one no longer has any obligation to pay it. Notify the Tax Collector’s office of the change and confirm who is responsible. If the bill goes unpaid, penalties attach to the property regardless of whose mistake it was.

Your lender must send an annual escrow statement showing all disbursements within 30 calendar days of the end of the escrow computation year.⁹ Match the tax entries against what the county shows as paid.

How to Pay Before the Deadline

The Treasurer-Tax Collector accepts payment several ways:

Online by e-check through the county portal, with no service fee. This is the cheapest electronic option.¹⁰
Online by credit or debit card, PayPal, Apple Pay, Venmo, or Google Pay. These carry a 2.50% service fee with a $3.50 minimum. On a $5,000 bill, that is an extra $125.¹⁰
By mail to Contra Costa County Treasurer-Tax Collector’s Office, 625 Court Street, Room 100, P.O. Box 631, Martinez, CA 94553. Mail early enough that the postmark lands on or before the delinquency date.¹¹
In person at the Finance Building in Martinez during business hours, or in the secure drop box outside after hours.

A bounced e-check brings a returned-payment fee of up to $85, and you lose credit for the attempted payment.¹¹ Verify the routing and account numbers before you submit. You’ll need your Assessor’s Parcel Number (APN) from the tax bill, which you can also look up on the county Assessor’s or Tax Collector’s website by property address.¹²

1
California Legislative Information. California Code Revenue and Taxation Code 2617
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California Legislative Information. California Code Revenue and Taxation Code 2618
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Contra Costa County. New Property Owners
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California Legislative Information. California Code Revenue and Taxation Code RTC 2619
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California Legislative Information. California Code Revenue and Taxation Code RTC 2512
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Contra Costa County. Frequently Asked Questions
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California Legislative Information. California Code Revenue and Taxation Code 4103
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California State Controller’s Office. Public Auctions and Bidder Information
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Consumer Financial Protection Bureau. Escrow accounts
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Contra Costa County. Electronic Payment Service Fee Structure
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Contra Costa County Treasurer and Tax Collector. Account Lookup and Installment Options
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Contra Costa County. Frequently Asked Questions