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Contra Costa County Property Tax Guide for Homebuyers (2026)

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Contra Costa County Property Tax Guide for Homebuyers (2026)

Contra Costa County Property Tax Guide for Homebuyers (2026)

By James Quintero, Founder, Rise Group Real Estate — CA DRE #02051216 — Published August 7, 2026

Modern single-family suburban home with a driveway and neat front yard, representing a Contra Costa County property subject to California property tax

Property tax is the line item that surprises more Contra Costa homebuyers than any other. You budget for the down payment and the mortgage, and then a supplemental bill lands in the mailbox six months after closing for a number nobody warned you about. This guide walks through how California property tax actually works, what you’ll pay by city, how Mello-Roos and supplemental bills change the math, and which exemptions can trim the total. The goal is simple: no surprises after you get the keys.

Key Takeaways

  • A new Contra Costa buyer should budget roughly 1.1% to 1.3% of the purchase price per year — the 1% Proposition 13 base rate plus voter-approved bonds (CA Board of Equalization, retrieved 2026-07-09).
  • Under Proposition 13, your assessed value resets to your purchase price when you buy, then can rise no more than 2% a year.
  • Newer developments in Brentwood and Antioch often carry Mello-Roos special taxes that add roughly $1,200–$3,500 a year on top of the base rate.
  • Expect a one-time supplemental tax bill after closing, and file the $7,000 Homeowners’ Exemption to shave a little off every year (CA BOE, retrieved 2026-07-09).

Please note: This article is general information for East Bay homebuyers, not tax or legal advice. Property tax outcomes depend on your specific parcel and situation. Confirm any figure with the Contra Costa County Assessor and consult a qualified tax professional before making decisions.

What Is the Property Tax Rate in Contra Costa County?

In 2026, a Contra Costa homebuyer should plan on paying about 1.1% to 1.3% of the purchase price in annual property tax. That’s the 1% base rate set by Proposition 13, plus voter-approved bond debt for schools and local projects (CA Board of Equalization, Publication 800-10, retrieved 2026-07-09). Mello-Roos areas run higher.

Here’s the trap that catches people. Search “Contra Costa property tax rate” and you’ll see figures like 0.85% of home value quoted as the county average (SmartAsset, retrieved 2026-07-09). That number is real, but it isn’t your number. It averages in longtime owners whose Proposition 13-protected assessed values sit far below today’s prices. As a new buyer, your assessed value equals what you just paid — so you should budget from the full 1.1%–1.3%, not the historical average.

What we tell buyers at Rise Group: ignore the “average effective rate” headlines. A neighbor who bought in 1995 might pay 0.4% of their home’s current value; you’ll pay closer to 1.2% because your bill is built on your 2026 price, not theirs. Two identical houses on the same street routinely have wildly different tax bills for exactly this reason.

How Proposition 13 Sets Your Assessed Value

Proposition 13, passed in 1978, caps the base property tax at 1% of a property’s assessed value and limits annual increases in that assessed value to 2% per year (CA Board of Equalization, retrieved 2026-07-09). The catch for buyers is the reassessment trigger: when a home changes ownership, the county resets its assessed value to the current market value, which is essentially your purchase price.

What does that mean in practice? If you buy for $900,000, your assessed value becomes $900,000 the day you close, regardless of what the previous owner was paying tax on. From there, the assessment can climb at most 2% annually, which is why long-tenured owners enjoy such low bills. It’s a homeowner-friendly system once you’re in — but the reset at sale is exactly why your first bill jumps compared to the seller’s.

Because the assessment is anchored to your price, property tax is one of the few costs you can estimate accurately before you even make an offer. Multiply the purchase price by roughly 1.2% for a working annual number, then refine it once you know the specific tax rate area and any special assessments on the parcel. For where this fits among your other closing costs, see our East Bay home buying guide.

Effective Property Tax Rates by City in Contra Costa County

Across Contra Costa cities, estimated effective property tax rates cluster between roughly 1.2% and 1.35% of value, with Brentwood and Antioch trending higher once Mello-Roos enters the picture (Ownwell property tax data, retrieved 2026-07-09). The base rate is nearly identical everywhere; what moves the needle is local bond debt and special taxes.

The table below shows estimated all-in effective rates by city, plus whether Mello-Roos commonly appears in newer developments there. Treat the percentages as directional planning figures, not official assessments — the authoritative starting point is always 1% plus voter-approved bonds.

City Est. Effective Rate* Mello-Roos Common? Notes
Walnut Creek ~1.21% Rare Varies by ZIP; older core, few special taxes
Antioch ~1.23% Yes (newer tracts) East County; CFDs common in newer subdivisions
Pleasant Hill ~1.24% Rare Established neighborhoods, mostly base rate
Concord ~1.29% Rare Largest city in the county by population
Brentwood ~1.32% Yes City has multiple Community Facilities Districts
Martinez ~1.32% Rare County seat

*Estimated all-in effective rates as a percentage of value, including voter-approved bonds but excluding parcel-specific Mello-Roos. Source: Ownwell, retrieved 2026-07-09. Official base rate (1% + bonds) per CA BOE.

Estimated Effective Property Tax Rate by City, Contra Costa County (2026) Horizontal bar chart showing estimated effective rates from about 1.21% in Walnut Creek to 1.32% in Brentwood and Martinez, versus a 1.02% national median. Estimated Effective Property Tax Rate by City (2026) % of home value, incl. voter-approved bonds. Amber = Mello-Roos common. Source: Ownwell, BOE (2026)

0% 0.5% 1.0% 1.5%

U.S. median 1.02%

Walnut Creek 1.21%

Antioch 1.23%

Pleasant Hill 1.24%

Concord 1.29%

Brentwood 1.32%

Martinez 1.32%

Estimated effective rates as a share of home value. Base rates barely differ city to city — Mello-Roos (amber) is what pushes Brentwood and newer Antioch tracts higher. Source: Ownwell and CA BOE, 2026.

Notice how close the bars are. The lesson for buyers comparing our East Bay community guides is that the base rate won’t make or break your decision between, say, Concord and Pleasant Hill. Mello-Roos will — so that’s the number to hunt down before you write an offer.

What Is Mello-Roos, and Do Brentwood Homes Have It?

Yes, many Brentwood homes have Mello-Roos, and so do newer developments in Antioch, Oakley, and Discovery Bay. Mello-Roos is a special tax created under the Community Facilities Act of 1982 to fund infrastructure — roads, schools, parks — in newer subdivisions, and it’s added on top of the 1% base rate (CA Board of Equalization, retrieved 2026-07-09). The City of Brentwood alone administers multiple Community Facilities Districts.

Unlike the base tax, Mello-Roos isn’t based on your home’s value — it’s a fixed special tax tied to the parcel and the bonds funding your neighborhood’s infrastructure. Typical amounts run roughly $1,200 to $3,500 per year, though the exact figure is parcel-specific and can push an area’s effective rate well past 1.5%. These taxes usually last 20 to 40 years until the bonds are repaid.

When we represent buyers in Brentwood’s newer tracts, checking Mello-Roos is a standard step before writing an offer — and it’s saved clients from payment shock more than once. Two similar homes a few miles apart can differ by $3,000 a year purely on special taxes. California law requires sellers to disclose Mello-Roos, and buyers of brand-new homes receive a formal Notice of Special Tax. Always read it, and factor the amount into your monthly budget. Our Brentwood community page is a starting point, but the parcel-level tax bill is where the real answer lives.

What Is a Supplemental Tax Bill?

A supplemental tax bill is a one-time (sometimes two-time) charge issued after you buy, capturing the difference between the seller’s old assessed value and your new, higher one, prorated for the remainder of the fiscal year (Contra Costa County, Supplemental Property Taxes, retrieved 2026-07-09). It arrives separately from your regular bill, and it catches almost every first-time buyer off guard.

Here’s why it exists. When you buy, the county reassesses the home to your purchase price, but the regular tax bill for that year was already calculated on the seller’s lower value. The supplemental bill trues up the difference from your closing date through June 30, the end of the fiscal year. If your purchase closes between January 1 and May 31, you may receive two supplemental bills — one for the current year and one for the next.

The amount can be substantial. Buy a home reassessed $400,000 above the seller’s old value at roughly 1.2%, and the annualized supplemental runs near $4,800, prorated for the months you owned it. Set money aside for this, because your lender’s escrow account usually won’t cover the supplemental bill — it’s typically your responsibility to pay directly.

Which Property Tax Exemptions Can Homebuyers Claim?

The exemption nearly every buyer qualifies for is the Homeowners’ Exemption, which reduces your assessed value by $7,000 — about $70 to $80 in annual savings (CA Board of Equalization, retrieved 2026-07-09). It’s modest, but it’s free money you claim once by filing a simple form. File by February 15 to capture the full exemption for the year.

Hand holding a set of keys to a newly purchased Contra Costa County home during closing

Beyond the standard exemption, a few programs help specific buyers:

  • Disabled Veterans’ Exemption: for 2026, this exempts $180,671 of assessed value (basic), or $271,009 for qualifying low-income veterans with household income at or below $81,131 (CA BOE, Letter to Assessors 2025/014, retrieved 2026-07-09). That’s a meaningful reduction, not a token one.
  • Seniors (55+): California has no blanket senior exemption, but Proposition 19 lets homeowners 55 and older transfer their existing lower assessed value to a new primary residence anywhere in the state, up to three times (CA BOE, Proposition 19, retrieved 2026-07-09). For a downsizing empty-nester, this can be worth thousands a year.
  • Property Tax Postponement: homeowners 62 or older, or blind or disabled, with household income at or below $55,181 may defer payment through the State Controller’s program at 5% simple interest (CA State Controller, retrieved 2026-07-09).

Eligibility rules for these programs are detailed, and deadlines matter. This is exactly the kind of decision to run past a tax professional or the County Assessor before you count on the savings.

When Are Contra Costa Property Taxes Due?

Contra Costa property taxes are paid in two installments: the first is due November 1 and delinquent after December 10, and the second is due February 1 and delinquent after April 10, with a 10% penalty on late payments (Contra Costa County, Secured Property Taxes, retrieved 2026-07-09). The tax year runs July 1 through June 30.

A handy way to remember the deadlines: “No Darn Fooling Around” — November, December, February, April. Miss a deadline and that 10% penalty is automatic, so calendar reminders are worth setting even if you think you’ll remember.

Most buyers never touch these dates directly, though. If you finance with less than 20% down — or take an FHA or VA loan — your lender will likely require an escrow (impound) account, collecting a slice of your property tax and homeowners insurance with each monthly mortgage payment and paying the bills on your behalf (Consumer Financial Protection Bureau, retrieved 2026-07-09). It smooths a big semiannual bill into twelve manageable pieces. Just remember the supplemental bill usually falls outside escrow.

Worked Example: Property Tax on a Median Walnut Creek Home

Let’s run the numbers on a median-priced Walnut Creek home, around $949,000 as of mid-2026 (Redfin, Walnut Creek market, retrieved 2026-07-09). This is illustrative — your actual bill depends on the exact tax rate area and any special assessments — but it shows the shape of what to expect.

Aerial view of a suburban residential neighborhood with winding streets and single-family homes

On a $949,000 purchase, your assessed value becomes $949,000 the day you close. Here’s the rough math:

  • 1% Proposition 13 base: $9,490 per year
  • Voter-approved bonds (to ~1.21% all-in): roughly $11,485 per year
  • Less Homeowners’ Exemption: about $85 back, netting near $11,400
  • Monthly, via escrow: roughly $950 folded into your mortgage payment

Then add the one-time supplemental bill. Because Walnut Creek’s older core rarely carries Mello-Roos, this estimate holds reasonably well — but a comparable home in a newer Brentwood tract could add $1,200–$3,500 a year in special taxes on top. Want the precise figure for a specific home, or a current estimate of your own property’s value? Start with a free home valuation, and browse pricing on our Walnut Creek homes page.

A Note on Tax Advice

Property tax rules in California are detailed, and small differences between parcels, ownership structures, and exemption eligibility can change your outcome. Everything here is general education to help you plan — it is not tax, legal, or financial advice. For questions about your specific situation, contact the Contra Costa County Assessor and a licensed tax professional. When you’re ready to talk homes and neighborhoods, that’s where our team can help.

Frequently Asked Questions

What is the property tax rate in Contra Costa County?

New buyers should budget roughly 1.1% to 1.3% of the purchase price per year — the 1% Proposition 13 base rate plus voter-approved bonds (CA BOE, 2026). Published “average” rates near 0.85% look lower because they include longtime owners with Prop 13-protected assessed values well below current market prices.

What is a supplemental tax bill?

A supplemental tax bill is a one-time charge issued after you buy, covering the difference between the seller’s old assessed value and your new purchase-price assessment, prorated to the end of the fiscal year (Contra Costa County, 2026). Buyers closing between January and May can receive two supplemental bills, and escrow usually doesn’t cover them.

Do Brentwood homes have Mello-Roos?

Many newer Brentwood homes do. Mello-Roos is a special tax funding infrastructure in newer developments, added on top of the 1% base rate and typically running $1,200–$3,500 a year (CA BOE, 2026). Antioch, Oakley, and Discovery Bay tracts often carry it too. Sellers must disclose it, so verify the exact amount before you offer.

How does Proposition 13 affect my property taxes when I buy?

When you buy, Proposition 13 resets the home’s assessed value to your purchase price, then caps annual increases at 2% (CA BOE, 2026). That’s why your first bill is often higher than the seller’s — theirs reflected a lower, older assessment. Your assessment is built on what you paid in 2026.

Can I lower my Contra Costa property tax bill?

Most owners can file the $7,000 Homeowners’ Exemption for about $70–$80 in yearly savings (CA BOE, 2026). Disabled veterans, seniors transferring value under Proposition 19, and income-qualified owners using the state Postponement program may save more. Confirm eligibility with the County Assessor or a tax professional.

About the Author: James Quintero is the Founder of Rise Group Real Estate, an independent East Bay brokerage headquartered in Walnut Creek with 30+ agents serving Walnut Creek, Concord, Brentwood, Martinez, Pleasant Hill, Antioch, and the surrounding Contra Costa County market. CA DRE #02051216. This guide is provided for general educational purposes and is not tax or legal advice.

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