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Guide

Contra Costa Property Tax Explained

By Karla I. Vasquez, REALTOR® · Keller Williams Realty Danville · Reviewed October 2026

Quick answer

In Contra Costa County, your property tax starts with a 1% general tax on your assessed value, plus any voter-approved bond rates for your area, plus special assessments for local services. Under Proposition 13, your assessed value is generally set when you buy or build, then can rise by no more than 2% a year. The annual bill is paid in two installments, due November 1 and February 1.

How is property tax calculated in Contra Costa County?

The County Treasurer-Tax Collector explains it in three parts:

  1. Ad valorem tax (value-based): The Assessor's value for your property is multiplied by the tax rate. The rate is the countywide 1% general tax plus any general obligation bond rates.
  2. Exemptions: Some exemptions reduce your assessed value, such as the homeowners' exemption.
  3. Special assessments: Charges for services or benefits to your property, such as sewer, garbage, street lighting, landscaping, mosquito abatement or fire protection.

Because bond rates come from the specific districts where your home is located (often school construction bonds), two homes with the same value in different parts of the county can have different total tax rates.

What Prop 13 means for you

The State Board of Equalization summarizes the key rules:

  • Base value: Property is reassessed to market value when there's a change in ownership or when new construction is completed.
  • Annual limit: After that, assessed value generally increases with inflation, capped at 2% per year.
  • Rate: The general tax is 1% of taxable value, plus amounts to repay voter-approved debt.

That's why long-time owners on the same street can pay very different taxes than a new buyer.

What if values drop? If market value falls below your assessed value, the Contra Costa Assessor offers a free informal value review (often called a Prop 8 review). Formal appeals go to the Assessment Appeals Board, with filing deadlines.

Due dates and penalties

The fiscal tax year runs July 1 through June 30, and the annual secured bill is mailed by November 1.

  • 1st installment: due November 1, delinquent after December 10 (covers July–December).
  • 2nd installment: due February 1, delinquent after April 10 (covers January–June).
  • Penalties: 10% on a late first installment; 10% plus a $20 administrative charge on a late second installment.
  • Partial payments: The County does not accept them; underpayments are returned.
  • Paying early: You can pay both installments by December 10.

Not receiving a bill doesn't excuse a late payment. If you just bought, look up your parcel online with your APN or call the Tax Collector's office.

The $7,000 homeowners' exemption

If the home is your principal residence, you can claim a $7,000 reduction in assessed value, which lowers your annual bill by at least $70. New owners typically receive an application from the Assessor within several months of purchase. Return it promptly. You file once; it stays as long as you own and live in the home.

Karla's tips

  • Look at the real bill, not the listing estimate. Ask for the current tax bill and check for bonds and special assessments that may carry over to you.
  • Budget for the reassessment. When you buy, your taxes will be based on your purchase price, not the seller's older value. See my guide on supplemental tax bills.
  • Know your impound setup. If your lender pays your taxes, confirm they have the right parcel information each year.
  • Remodeling? Plan for new construction. As Owner & Principal of KCK Construction & Remodeling, I remind clients that completed additions can add value to your assessment. Repairs and maintenance are treated differently, so ask the Assessor before you build.
  • Spanish help. If you'd like help reading your tax bill in Spanish, call me at (510) 677-8695.

En español: lo básico

En el Condado de Contra Costa, el impuesto a la propiedad comienza con un 1% del valor tasado, más los bonos aprobados por los votantes y cargos especiales por servicios locales. Bajo la Proposición 13, el valor se fija cuando usted compra o construye, y después normalmente sube como máximo 2% al año. El pago se divide en dos partes: vence el 1 de noviembre (morosa después del 10 de diciembre) y el 1 de febrero (morosa después del 10 de abril). Si la casa es su residencia principal, solicite la exención de propietario de $7,000.

Sources

General information only, not legal, tax or financial advice. Rules and fees change; confirm with the County, the Board of Equalization, your tax professional or an attorney. Karla I. Vasquez is a REALTOR® and Registered LDA, not an attorney.