The property tax clock in Contra Costa and Alameda, and why slow is the trap

The mortgage clock is loud. The property tax clock hardly makes a sound, and that is the whole problem with it.

A woman in Antioch once put a county envelope on my desk that had been opened, read, and folded back into its envelope four times. She had been carrying it in her purse for a year and a half. The bill inside wasn't large. What it had grown into was.

Two installments and a 10% penalty

California secured property taxes come in two halves. The first installment is due November 1 and goes delinquent after December 10. The second is due February 1 and goes delinquent after April 10. Miss either date and a 10% penalty is added to that installment, and the second one picks up a cost charge on top. The Contra Costa County Tax Collector publishes the exact fees, and the Alameda County property tax portal does the same for owners on the other side of the county line. The dates are state law, so they don't change from county to county. The fee amounts do.

If your mortgage has an impound account, the servicer pays these and you never see the envelope. A lot of the people I saw had refinanced or paid the loan off and hadn't realized the envelope was now theirs to open.

July 1: tax-defaulted

Whatever is still unpaid when the fiscal year ends on June 30 gets declared tax-defaulted on July 1. The county records that status. Nothing is taken from you that day. What starts is the redemption penalty, which in California runs at 1.5% per month on the unpaid tax, plus a redemption fee. That's 18% a year, and it doesn't pause while you think it over.

The State Board of Equalization's property tax overview explains the framework the counties work inside, if you want the statute-level version.

Five years before the tax collector can sell

Here's the part that makes people relax when they shouldn't. The tax collector can't sell a defaulted home for at least five years after it becomes tax-defaulted. Five years sounds like forever. It isn't. It's five years of 18% penalty piling onto the original amount while the current year's bill also goes unpaid, because a household that couldn't pay last year usually can't pay this year either.

At the end of the five years the property becomes subject to the tax collector's power to sell, and Contra Costa holds its sales of tax-defaulted property periodically, with notice mailed and published beforehand. The opening bid is built on the taxes owed plus costs, which is usually a fraction of what the house is worth, and what you get afterward is a claim process for the excess.

The five-year installment plan

The county would rather be paid than sell. So there is a redemption installment plan: you put down a portion of the defaulted amount plus the fees, agree to pay the rest in yearly installments over up to five years, and, this is the part people miss, you keep every new year's tax bill current on top of it.

Miss one installment or one current bill and the plan defaults and the whole balance comes back. I had a man from Pittsburg who opened a plan twice and lost it twice on the second-installment date in April, because April was when his business had no work. If your income is seasonal, plan the plan around that.

The plan has to be started before the power to sell attaches. Don't wait until year five to call the tax collector.

How the default shows up when you try to sell

A tax default is a lien, and it's the first thing a title company finds. When escrow opens on your house, the preliminary title report lists the defaulted taxes, the redemption penalty to date, and the fees. The sale can't close until that number is paid, and escrow pays it out of the sale proceeds at closing. No buyer's lender will fund around it. No cash buyer will either.

That's also the good news. An owner who decides to sell a house with back taxes for cash doesn't need to come up with the money first. Escrow orders the payoff from the county, pays it at closing, and the owner gets what's left. I've seen more than one Antioch sale close where the tax default was the only lien, and the seller walked away with most of the price.

Supplemental bills catch people

When you buy a house or finish an addition, the assessor reassesses it and sends a supplemental bill for the difference between the old value and the new one, prorated for the rest of the year. It comes separately, on its own due dates, and an impound account usually doesn't pay it. A lot of the tax defaults I saw in Pittsburg started this way: someone bought in the spring, got a supplemental bill in the fall, assumed the mortgage company had it, and found out two years later that nobody did.

A worked example from Antioch

Say the annual bill is $6,000, and both installments for 2025-26 were missed. That's $600 in penalties plus the cost charge. On July 1, 2026 the $6,000 goes into default and the redemption penalty starts: $90 a month, $1,080 a year. Three years on, the redemption figure is around $9,800 plus fees, and three more years of current bills are sitting next to it if they went unpaid too. That's closer to $28,000 against a bill that started at six.

Those are my example numbers, not a quote from the county. Run your own parcel through the county's portal for the real ones.

What the city and the courts can and can't do

The City of Antioch doesn't collect property tax and can't set up a plan for you. Calling city hall gets you a polite redirect to the county at Martinez. If the default has gotten tangled up with something else, a death in the family and a deed in the wrong name, an eviction, a co-owner who won't sign, the California courts' self-help housing pages are the place to start, and they're free.

None of this is tax or legal advice for your situation. It's the general shape of the timeline as I learned it from years of watching it run.

My judgment on the tax clock

The tax default is the debt where waiting costs the most and feels the cheapest. If the house has equity and the household can't get current and stay current, the right move is to sell before the redemption figure eats the equity, not in year five. When I had a family in that spot, we'd start by asking the tax collector for a redemption figure good through a specific date, then get numbers from cash home buyers in Solano and Contra Costa who will pay the defaulted tax through escrow. The county is paid at closing and the family gets what's left.