How to Pay Your Contra Costa County Property Tax Bill
Where to send your Contra Costa property tax payment
Contra Costa County Assessor's Office collects property taxes and sends you a bill twice a year—usually in August and February. You can pay by mail, online, in person, or through automatic withdrawal. The county does not require you to pay through any single method, so you can choose what works for your household.
Mail payments to the address printed on your bill. If you pay online, go to the county's official tax payment portal (accessible through the Assessor's Office website). In-person payments are accepted at the Assessor's Office in Martinez during business hours, and some county offices accept payments as well. Automatic withdrawal—called an ACH debit—pulls money directly from your bank account on a date you choose, and you set it up once through the online portal.
The key difference between methods is timing. Mail takes 7 to 10 business days to reach the county, so if your bill is due soon, mailing late can result in a late payment even if you sent the check on time. Online and automatic payments post within one to two business days. In-person payments are recorded immediately.
Key Takeaways
- Contra Costa sends property tax bills twice yearly, and you can pay by mail, online, automatic bank withdrawal, or in person at the Assessor's Office.
- Mail payments take 7 to 10 business days to reach the county, so online or automatic payment is safer if your due date is approaching.
- A late payment triggers a 10 percent penalty on the unpaid amount, plus interest that accrues monthly until the bill is paid in full.
- If you cannot pay the full amount by the due date, contact the Assessor's Office about a payment plan before the deadline passes.
- Homeowners over 65, disabled, or on a fixed income may be may be able to access for a property tax postponement that delays payment until the property is sold or transferred.
What happens if your payment is late
Contra Costa assesses a 10 percent penalty on any unpaid property tax balance after the due date. This penalty is added to your bill immediately. After that, interest accrues at a rate set by the state (currently around 0.5 percent per month, though this changes annually). Interest compounds monthly, meaning you pay interest on the interest.
If your bill remains unpaid for three years, the county can file a tax lien against your property. A lien is a legal claim that gives the county the right to sell your home to recover the unpaid taxes. Before that happens, you will receive notices and have opportunities to pay, but ignoring them does not stop the process.
The penalty and interest grow quickly. A $5,000 unpaid bill becomes $5,500 after the 10 percent penalty, and then interest begins accruing on the full $5,500. Paying as soon as you can—even if it is after the due date—stops the interest clock and prevents the lien from moving forward.
Payment plans and hardship options
If you cannot pay your full bill by the due date, contact the Contra Costa Assessor's Office before the deadline. The county offers installment agreements that let you split your payment into smaller amounts over several months. You must request this in writing or by phone, and the county will review your situation to determine whether a plan is possible.
Installment plans do not erase the penalty or interest, but they prevent additional penalties from accruing as long as you make each payment on time. If you miss a payment on the plan, the county can cancel it and demand the full remaining balance immediately.
If you are a homeowner over 65, blind, or disabled, you may be may be able to access for property tax postponement through the State Controller's Office. Postponement delays your tax payment until you sell the property, move, or pass away. Your heirs would then owe the postponed taxes from the estate. This program has income limits and other requirements, and you must apply through the state, not the county.
How to set up automatic payments
Log into the Contra Costa County Assessor's online payment portal and select the automatic payment option. You will need your property tax bill number (found on your bill) and your bank account details. The system will ask you to choose a payment date each month or a single date for the year.
Automatic payments are deducted via ACH, which is a bank-to-bank transfer that takes one to two business days to clear. Set your payment date at least three days before the county's due date to account for processing time. If your bank account does not have enough money on the scheduled date, the payment will fail and you will be charged a late fee by both your bank and the county.
You can change or cancel automatic payments anytime through the portal. If you cancel, you are responsible for paying manually by the next due date.
Understanding your property tax bill
Your Contra Costa property tax bill shows the assessed value of your property, the tax rate, and the total amount due. The bill also lists the due date and any penalties or interest from previous unpaid amounts. Read the bill carefully to make sure the property address and assessed value are correct—errors do happen, and you have the right to challenge them.
Property taxes in Contra Costa are based on the assessed value, which is usually set at the time you buy the property. The county reassesses when the property changes hands or when you make major improvements. The tax rate itself is set by the county and does not change year to year, but your bill can increase if your assessed value increases.
If you believe your assessed value is wrong, you can file a Proposition 8 application (a temporary reduction) or a formal assessment appeal. Both must be filed within 30 days of receiving your bill. The Assessor's Office website has forms and instructions for both processes.
Online payment portal and account access
The Contra Costa County Assessor's Office website has a secure portal where you can view your bill, make one-time payments, and set up automatic payments. You do not need to create an account—you can pay as a guest using your property tax bill number. If you want to save your information for future payments, you can register for an account with an email address and password.
The portal accepts credit cards, debit cards, and bank account transfers. Credit and debit card payments charge a convenience fee (usually 2 to 3 percent of the payment amount), but bank transfers and automatic payments do not. If you are paying a large bill, the fee difference can be significant.
If you lose your bill or need to look up your account information, you can search by property address or parcel number on the Assessor's website. The parcel number is a unique identifier assigned to your property and appears on your bill.
Mailing address and contact information
Mail property tax payments to the address printed on your bill. Do not send payments to the Assessor's Office main address unless your bill specifically directs you there—different departments handle different types of payments, and sending to the wrong address delays processing.
If you have questions about your bill, payment options, or hardship programs, contact the Assessor's Office directly. Phone numbers and office hours are listed on the county website. You can also visit in person at the main office in Martinez. Bring your bill or property address so staff can pull up your account quickly.
If you are disputing your assessed value or filing an appeal, follow the specific instructions on the Assessor's website. Appeals have strict deadlines, and missing them means you lose your right to challenge that year's assessment.
Frequently Asked Questions
Can I pay my property tax bill in installments without asking first?
No. You must contact the Assessor's Office and request an installment agreement before the due date. The county will not automatically set up a payment plan. If you pay late without an approved plan, the 10 percent penalty and interest will be added to your bill.
What if I pay online but the payment does not show up on my bill?
Online payments take one to two business days to post. If more than two business days have passed and the payment still does not appear, contact the Assessor's Office with your confirmation number from the payment portal. Keep that confirmation number until the payment is reflected on your account.
Do I have to pay property taxes if I am renting out my home?
Yes. The property owner is responsible for property taxes, regardless of whether the property is owner-occupied or rented. Tenants do not pay property taxes directly—the landlord pays them and typically covers the cost through rent.
Can I deduct my Contra Costa property taxes from my federal income tax?
You may be able to deduct state and local property taxes on your federal return, but there is a combined limit of $10,000 per year for all state and local taxes (including income tax and sales tax). Consult a tax professional or the IRS website to determine whether your situation qualifies.
What if I inherit property in Contra Costa—am I responsible for unpaid property taxes?
Yes. Unpaid property taxes become a debt against the property itself, not just the previous owner. As the new owner, you inherit the obligation to pay any back taxes, penalties, and interest. The county will send you a bill after the property is transferred to your name.