Whether you just closed on a home in Concord or have owned in Walnut Creek for years, understanding how Contra Costa County property taxes work can save you money and prevent surprise bills. This guide covers the current 2025-2026 tax rates, due dates, city-level breakdowns, how to pay online, and what to do if you think your assessment is too high.
What Are Property Taxes and How Are They Used?
Contra Costa County property tax is calculated as 1% of assessed value (the Proposition 13 base) plus voter-approved bonds and special assessments. Most homeowners pay a combined effective rate between 1.10% and 1.40% of assessed value. The first installment is due November 1 and becomes delinquent after December 10; the second installment is due February 1 and becomes delinquent after April 10. A 10% penalty applies immediately to any installment paid after the delinquency date.
Property taxes are annual charges levied by local government on real estate owners. In Contra Costa County, those revenues fund public schools, fire and police services, road maintenance, libraries, and other community infrastructure. For most homeowners, property taxes are one of the larger recurring costs of ownership alongside the mortgage payment itself.
How Much Is Property Tax in Contra Costa County?
California’s Proposition 13 sets the base property tax rate at 1% of a property’s assessed value statewide. On top of that base rate, Contra Costa County and its cities add voter-approved local assessments and bond measures. The result is an effective rate that varies by location.
For most properties in Contra Costa County during the 2025-2026 assessment year, the effective property tax rate falls between 1.10% and 1.40% of assessed value, depending on the city and applicable special assessments.
The county calculates your tax bill by multiplying your property’s assessed value by the applicable rate for your tax rate area (TRA). Your TRA is determined by your address and reflects which special districts, school bonds, and local measures apply to your property.
2025-2026 Property Tax Rates by City in Contra Costa County
Effective tax rates vary across Contra Costa cities because each area carries different voter-approved bond measures and special assessments. The figures below represent estimated effective rates for typical residential properties in each city. Your actual rate depends on your specific tax rate area.
| CITY | ESTIMATED EFFECTIVE TAX RATE | NOTES |
|---|---|---|
| Walnut Creek | 1.10% – 1.20% | Mostly older inventory, modest add-ons |
| Concord | 1.15% – 1.30% | Some Mello-Roos in newer subdivisions |
| Pleasant Hill | 1.10% – 1.20% | Mostly older neighborhoods |
| Lafayette | 1.10% – 1.20% | Mature inventory, low add-ons |
| Orinda | 1.10% – 1.20% | Established neighborhoods |
| Danville | 1.15% – 1.40% | Higher in newer Blackhawk and Tassajara areas (Mello-Roos) |
| San Ramon | 1.15% – 1.45% | Higher in Dougherty Valley (heavy Mello-Roos) |
| Brentwood | 1.20% – 1.65% | Newer master-planned communities; significant Mello-Roos |
| Antioch | 1.15% – 1.45% | Higher in newer subdivisions |
| Richmond | 1.15% – 1.30% | Standard West County rates |
| El Cerrito | 1.10% – 1.20% | Mature inventory |
| Martinez | 1.10% – 1.20% | County seat; standard rates |
To find the exact rate for your property, use the Contra Costa County Assessor’s property lookup tool and enter your parcel number or address.
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When Are Contra Costa Property Taxes Due?
Property taxes in Contra Costa County are billed annually but paid in two installments.
| INSTALLMENT | DUE DATE | DELINQUENT AFTER |
|---|---|---|
| First Installment | November 1 | December 10 |
| Second Installment | February 1 | April 10 |
Missing the December 10 or April 10 deadlines triggers a 10% penalty on the unpaid amount. If the second installment remains unpaid after June 30, the property may be subject to a tax lien. Not receiving a bill does not exempt you from these deadlines or penalties.
If you escrow your taxes through your mortgage, your lender handles these payments automatically from your monthly escrow deposit. Check your annual escrow analysis to confirm the correct amount is being collected.
How to Pay Contra Costa Property Taxes Online
The Contra Costa County Treasurer-Tax Collector’s Office accepts online payments through its official portal. You can pay by credit card, debit card, or e-check.
To pay online:
- Visit this website.
- Search for your property using your parcel number, address, or bill number
- Select the installment you want to pay
- Choose your payment method and complete the transaction
Keep your confirmation number. A convenience fee applies to credit and debit card payments; e-check payments are typically lower cost.
You can also pay by mail or in person at the Treasurer-Tax Collector’s Office located at 625 Court Street, Room 100, Martinez, CA 94553.
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What Are Supplemental Property Taxes?
When you purchase a home in Contra Costa County or complete new construction or major improvements, the county reassesses your property at its new market value. If the new assessed value is higher than the previous one, you’ll receive a supplemental tax bill for the difference.
Supplemental taxes are prorated based on how many months remain in the fiscal year (July 1 to June 30) from the date of ownership change or project completion. If you buy a home in January, for example, you’ll owe supplemental taxes covering roughly six months of the reassessment difference.
Supplemental bills are separate from your regular property tax bill and arrive on their own schedule. New homeowners sometimes miss them because they arrive months after closing. Watch for them and factor the cost into your budget.
How to Appeal Your Property Tax Assessment in Contra Costa County
If you believe your property has been assessed at more than its fair market value, you have the right to appeal. Many homeowners skip this step without realizing how straightforward the process is.
When to Consider an Appeal
An appeal makes sense when your property’s assessed value is higher than what comparable homes in your area actually sold for. This can happen after a rapid market correction, if the assessor used outdated data, or if there are property-specific issues (condition, access, easements) that weren’t accounted for.
How to File an Appeal
- Get your current assessed value. Find it on your property tax bill or through the Contra Costa County Assessor’s website.
- Gather comparable sales data. Pull recent sales of similar homes in your neighborhood to support your argument that the assessed value is too high.
- File an Application for Changed Assessment with the Contra Costa County Assessment Appeals Board. The standard filing window is July 2 through November 30.
- Attend your hearing. You’ll present your evidence to the board, and they will issue a decision.
If your appeal is successful, your assessed value will be reduced and you’ll receive a refund for any overpaid taxes. There is no penalty for filing an unsuccessful appeal.
For forms and filing instructions, visit the Contra Costa County Assessment Appeals Board.
Proposition 13 and Your Annual Tax Cap
Under California’s Proposition 13, the assessed value of your property can increase by no more than 2% per year as long as you own it and do not trigger a reassessment event. Reassessment events include a sale, transfer of ownership, or completion of new construction.
This cap is one of the most significant protections California homeowners have. It means a homeowner who has owned their property for 20 years may be paying taxes on an assessed value far below current market value, which is entirely legal and by design.
When you purchase a home, the assessed value resets to the purchase price. From that point forward, your annual increases are capped at 2% until the next qualifying change in ownership.
Frequently Asked Questions
What is the property tax rate in Contra Costa County?
Most Contra Costa County homeowners pay a combined effective property tax rate between 1.10% and 1.40% of assessed value. The rate starts with the 1% Proposition 13 base, then adds voter-approved bonds and special assessments specific to your Tax Rate Area. In Mello-Roos communities (Brentwood, Dougherty Valley in San Ramon, parts of Danville), the effective rate can climb to 1.50% or higher.
When are Contra Costa County property taxes due?
Contra Costa County property taxes are paid in two installments. The first installment is due November 1 and becomes delinquent after December 10. The second installment is due February 1 and becomes delinquent after April 10. A 10% penalty applies immediately to any installment paid after the delinquency date.
How do I pay my Contra Costa County property tax bill online?
Visit this online portal, search by parcel number, address, or bill number, then pay by e-check (typically lower cost) or credit/debit card (a third-party convenience fee applies). Save the confirmation number after the payment posts.
What is the Homeowners’ Exemption in Contra Costa County?
The Homeowners’ Exemption reduces the assessed value of your owner-occupied primary residence by $7,000, which saves roughly $70 per year. File Form BOE-266 with the Contra Costa County Assessor by February 15 of the tax year you want the exemption to apply. After February 15, you can still file but only receive 80% of the benefit for that year.
How do I appeal my Contra Costa County property tax assessment?
File an Assessment Appeal Application with the Contra Costa County Assessment Appeals Board between July 2 and November 30 of the tax year. For supplemental tax bills, you have 60 days from the date of the bill to file an appeal. Include comparable sales data and any supporting documentation.
What is a supplemental property tax bill in Contra Costa County?
A supplemental tax bill covers the difference between the prior owner’s assessed value and your new assessed value (typically your purchase price) after a sale or new construction. It is sent in addition to the regular annual tax bill, usually within several months of closing, and most lender escrow accounts do not cover it. Set aside cash to pay it out of pocket.
What happens if I pay my Contra Costa County property taxes late?
A 10% penalty is added to the unpaid installment immediately after the delinquency date. After June 30, the property moves to tax-defaulted status and additional penalties and interest accrue. After five years of default, the property may be sold at a tax sale.
Want to Learn More?
Property tax is a major component of your monthly housing payment, and getting the math right at the application stage prevents surprises after closing. If you are buying or refinancing in Contra Costa County and want a clear picture of your full monthly payment (including escrow for taxes, insurance, and any Mello-Roos), we can walk you through the numbers in 15 minutes.
If a refinance is on the table, particularly for debt consolidation, factor your full Contra Costa County tax bill into the new escrow analysis. A higher rate that lowers your total monthly payment can still be the right move.
Ready to talk through your Contra Costa home purchase or refinance? Contact JVM Lending today for a free rate quote.
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Please note: The information in this post is for educational purposes only. JVM Lending is not a tax professional or financial advisor. Property tax laws can be complex and vary by location. Consult a certified tax professional for personalized guidance. If you need a referral, contact us and we’ll connect you with a trusted professional in our network.
