By Paarth Shah, REALTOR® · August 17, 2026 · Contra Costa County
The short answer: 1 percent of your assessed value, plus voter-approved bonds, plus any direct assessments on your parcel. The first number is fixed statewide. The other two are why two homes with identical purchase prices in Contra Costa can carry noticeably different tax bills.
Under Proposition 13, your assessed value is generally set at what you paid for the home, and the county levies a 1 percent general tax against it. The county Auditor-Controller explains that on top of that base, each parcel is charged its share of general obligation bond rates, which are set annually from the debt service owed by the districts that issued the bonds and the assessed valuations inside those districts. Those rates can move every fiscal year, and no taxable property is exempt from them.
In practice, most Contra Costa bills land somewhat above 1 percent once bonds and assessments are added. JVM Lending's 2026 guide to the county puts the average effective rate at roughly 1.17 percent. Treat that as a planning figure, not your figure. Newer subdivisions in places like San Ramon and Brentwood may also carry Mello-Roos community facilities district charges, which fund local infrastructure and can add meaningfully to an annual bill. Those show up as separate line items, and they typically have an end date you can look up.
To find what a specific home actually pays, do two things before you write an offer. First, pull the parcel's current bill through the Contra Costa Treasurer-Tax Collector's online portal, which shows the itemized bonds and direct assessments rather than a countywide average. Second, remember that your bill will be recalculated after you buy: the assessor reassesses at your purchase price, and the difference between the seller's old assessment and your new one arrives as a supplemental bill, often several months after closing. Budget for it.
Payment timing catches new owners more than the rate does. The first installment of the secured bill is due November 1 and becomes delinquent after December 10. The second is due February 1 and becomes delinquent after April 10. A 10 percent penalty attaches immediately after each delinquency date, and no one waives it because your lender was slow or your escrow account was short. If you pay through an impound account, confirm in your first year that the payment actually went out.
If you want help comparing specific numbers against your situation, reach me through the contact page or at hello@homesbypaarth.com.
Contra Costa property tax starts at the Proposition 13 base rate of 1 percent of assessed value, plus voter-approved general obligation bonds and any direct assessments, which brings the average effective rate to roughly 1.17 percent in 2026. Newer subdivisions may also carry Mello-Roos charges.
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This is general market commentary, not financial, investment, or legal advice; figures are as of publication and can change. Verify specifics, including any school assignments, ratings, or boundaries, independently. Homes by Paarth is committed to Equal Housing Opportunity and does not steer clients toward or away from any neighborhood on the basis of a protected characteristic.