Alameda County property tax due dates fall on November 1 and February 1 each year, but the deadlines that actually matter are December 10 and April 10. Those are the delinquency dates. Pay by 5:00 p.m. on either one and you are on time; miss by a day and a 10 percent penalty attaches automatically, with no grace, no waiver, and no reminder.1Alameda County Treasurer-Tax Collector. Treasurer Tax Collector
The Two Installments
Alameda County bills property taxes once a year for the fiscal year that runs July 1 through June 30, and splits the bill into two payments.
The first installment is due November 1 and becomes delinquent after 5:00 p.m. on December 10. A 10 percent penalty attaches immediately.2California Legislative Information. California Revenue and Taxation Code 2617
The second installment is due February 1 and becomes delinquent after 5:00 p.m. on April 10. The penalty on the second installment is 10 percent plus a $10 administrative cost.3Justia. California Revenue and Taxation Code 2601-2636 – Collection Generally
The gap between the “due date” and the “delinquency date” is a built-in grace period, not two separate obligations. You can pay anytime from the due date up through 5:00 p.m. on the delinquency date. After that, it is late.
When December 10 or April 10 Falls on a Weekend or Holiday
If the delinquency date lands on a Saturday, Sunday, or legal holiday, the deadline shifts to 5:00 p.m. on the next business day. The same rule applies to supplemental bills. The extension is automatic, but the county does not send a notice about it, so check a calendar before you rely on the printed date.4California Legislative Information. California Revenue and Taxation Code 75.52
Supplemental Bills Run on a Different Clock
If you bought a home or finished new construction, the county reassessed the property and sent a supplemental tax bill. Those bills do not follow the November/February cycle. Their deadlines depend on when the county mailed the bill.
- Supplemental bills mailed July through October use the standard December 10 and April 10 delinquency dates.4California Legislative Information. California Revenue and Taxation Code 75.52
- Supplemental bills mailed November through June have a first installment that becomes delinquent at 5:00 p.m. on the last day of the month after the month the bill was mailed. The second installment becomes delinquent on the last day of the fourth month after that.4California Legislative Information. California Revenue and Taxation Code 75.52
A bill mailed in January, for example, has a first-installment delinquency date of the last day of February and a second-installment delinquency date of the last day of June. The exact dates print on the bill itself. New homeowners who file the supplemental notice with their closing paperwork and forget it are the ones who find out about the penalty months later.
What Late Payment Actually Costs
The penalty is 10 percent of the delinquent installment, applied the moment the deadline passes. On a $5,000 installment, that is $500 for being one day late. The second installment carries the same 10 percent plus a flat $10 cost.1Alameda County Treasurer-Tax Collector. Treasurer Tax Collector The county does not waive these penalties for forgetting, being out of town, or a check lost in the mail.
If taxes stay unpaid through the end of the fiscal year, the property is declared in default on July 1.5California Legislative Information. California Revenue and Taxation Code 3436 From that point, a redemption penalty of 1.5 percent per month, or 18 percent per year, accrues on the unpaid balance. Each new year of unpaid taxes starts its own 1.5 percent monthly charge on top.
Residential property that remains in default for five years can be sold at tax auction. For non-residential commercial property, the clock is three years.6California Legislative Information. California Code RTC 3691 At auction, the county can sell to any qualified bidder regardless of existing liens.
How to Pay Before the Deadline
There are three ways to pay, and after a recent postal change, they are no longer equally safe.
Online
The county’s online portal accepts e-checks from a checking or savings account at no cost, and credit cards with a 2.3 percent convenience fee.7Alameda County’s Official Website. Property Taxes Save the confirmation screen as your receipt. Have your Assessor’s Parcel Number ready; it appears on your tax bill and identifies your property in the county’s system.8Alameda County Assessor. Assessor’s Parcel Viewer and Parcel Maps
By Mail (Read This Before You Send a Check)
The county treats the USPS postmark on your envelope as the payment date. A postmark on or before the delinquency date is timely. Private postage meters and printed postage do not create a USPS postmark and can leave your payment classed as late if it arrives after the deadline.
A change that took effect on December 24, 2025 makes this riskier than it used to be. The USPS now applies postmarks when mail reaches an automated sorting facility, not when you drop it in a mailbox or hand it to a carrier. Depending on how far you live from a regional processing center, the postmark can land one to three days after you mailed the envelope.9IRS Taxpayer Advocate Service. New USPS Postmark Rules Could Affect if Your Tax Filing Is Considered on Time If you mail your payment, go to a USPS retail counter and ask for a manual postmark, or send it Certified Mail so you have documented proof of the mailing date.10State of California Franchise Tax Board. CA FTB Advises Taxpayers on USPS Postmark Updates and Filing Deadlines Dropping a check in a blue collection box on April 10 is no longer a safe bet.
Write your Assessor’s Parcel Number and installment number on the memo line, and include the detached payment stub.
In Person or Drop Box
The Treasurer-Tax Collector’s office is at 1221 Oak Street, Room 131, Oakland, CA 94612. A drop box at the building entrance is available Monday through Friday, 8:30 a.m. to 4:30 p.m., excluding county holidays. Do not put cash in the drop box.11Alameda County. Alameda County Property Tax News and Announcements
If Your Mortgage Lender Pays Through Escrow
Many owners never see the bill because the lender collects taxes monthly in escrow and pays the county directly. The lender is responsible for paying on time, but any penalty for a missed deadline attaches to your parcel, not to the bank. Check your annual escrow statement to confirm both installments were paid, and watch for shortage notices after reassessments or rate changes.
If You’ve Already Missed a Deadline
Once you are delinquent, pay as soon as you can to stop additional charges. If the balance is more than you can clear at once, Alameda County offers an installment payment plan under California Revenue and Taxation Code sections 4186 through 4337. To start one, you pay 20 percent of the total redemption amount, a $75 initiation fee, and all current-year taxes and supplemental bills in full. The remaining balance goes on monthly installments. You have to apply before the property has been in default for five years or before it becomes subject to the tax collector’s power to sell.12Alameda County Official Website. Application to Enter Into an Installment Payment Plan
The plan is not forgiveness. You still owe the full amount, and a missed plan payment can void the agreement. What it does is halt the compounding and give you a defined path back to a current account.