The first installment of your secured property tax bill is due November 1 and becomes delinquent at 5:00 p.m. on December 10, when a 10% penalty is added automatically. The second installment is due February 1 and delinquent after April 10, with a 10% penalty plus a $40 cost if it's missed. If you bought your home this year, you may also owe a separate supplemental tax bill covering the gap between the old assessed value and your purchase price, on top of your regular bill.

By Kat Bedbury and The Bedbury Group | October 27, 2026

Every year around this time, I hear from a few clients who either forgot the deadline entirely or didn't realize a second bill was coming. Neither mistake is expensive to avoid, but both get expensive fast if you miss them. With December 10 about six weeks out, now's the right time to get ahead of it.

This matters even more this year than usual. With homes on the Peninsula selling quickly and competitively over the past couple of months, a lot of people closed on a purchase recently, which means a lot of people are about to meet the supplemental tax bill for the first time, often without realizing it's coming.

The Two Deadlines Every Peninsula Homeowner Should Know

California splits your annual property tax bill into two installments, and San Mateo County's Tax Collector lays out the schedule plainly:

• First installment: Due November 1. Delinquent at 5:00 p.m. on December 10. Miss it, and a 10% penalty is added.

• Second installment: Due February 1. Delinquent at 5:00 p.m. on April 10. Miss it, and you'll owe a 10% penalty plus a flat $40 cost.

• If it's still unpaid after that, the county adds a $35 redemption fee on July 1, plus a 1.5% penalty every month it stays unpaid.

A couple of details worth knowing if you're paying by mail: your payment needs a U.S. Postal Service postmark on or before the delinquent date. A date stamped by a private postage meter doesn't count, only the actual USPS postmark does. And if a deadline falls on a weekend or holiday, you get until 5:00 p.m. the next business day before the penalty kicks in.

This schedule applies statewide under California law, so it's the same December 10 and April 10 pattern whether you're in San Mateo County or Santa Clara County, even though each county's tax collector handles its own billing and payments separately.

If You Bought a Home This Year, Watch for a Supplemental Tax Bill

This is the part that catches new buyers off guard most often, and given how fast homes have been selling on the Peninsula lately, a lot of people fall into this category this year.

Here's the mechanism: your regular property tax bill is based on your home's assessed value as of January 1 of the fiscal year. But when you buy a home, the county reassesses it at your purchase price right away, not the following January. That gap between the old assessed value and your new purchase price gets billed separately, as a supplemental tax bill, covering the remaining months of the fiscal year (which runs July through June).

A few things to expect if you bought this year:

• You'll likely get a Notification of Supplemental Assessment first, about 60 days before the actual bill, so it shouldn't come as a total surprise if you're watching your mail.

• You may receive more than one supplemental bill, depending on when your purchase happened relative to the fiscal year. A purchase that spans two fiscal years can generate a bill for each one.

• The amount is prorated, based on how many months remain in the fiscal year when the reassessment happens. It's not simply the full difference in value taxed at the full rate; it's that difference times the fraction of the year remaining, times the tax rate (generally around 1%, plus any voter-approved local measures).

• It's due when mailed, not on a fixed calendar date. Bills mailed between July and October follow the regular December 10 and April 10 deadlines. Bills mailed later follow a different schedule tied to when they were actually sent, so check your specific bill for its own due dates rather than assuming December 10 applies.

Here's a simplified, purely illustrative example of how the math works, not a calculation for any specific property: say a home was assessed at $900,000 as of the prior January 1, and you bought it for $1,500,000 in March, with four months left in the fiscal year. The county would prorate roughly 4/12 of the $600,000 difference, about $200,000, and apply the tax rate to that amount for the supplemental bill. The real number on your own bill depends on your actual purchase price, assessed value, closing date, and local tax rate, so treat this only as a way to understand the mechanism, not as a stand-in for your actual bill.

If you closed on a home anytime in the past year and haven't thought about this, it's worth checking directly with the county assessor's office for your specific purchase date, rather than guessing at the amount or timing. This is also the kind of thing that's easy to miss amid everything else involved in a recent purchase, so a quick check now can save you a penalty later.

What to Do Before December 10

A short checklist, whether you're a longtime owner or you bought this year:

1. Confirm the county has your current mailing address. If you moved recently or your bill goes to an old address, you can miss a deadline simply because the bill never reached you. This isn't an excuse the county accepts; it's still your responsibility to pay on time.

2. Check whether your mortgage includes an escrow or impound account. Many lenders collect property taxes as part of your monthly mortgage payment and pay the county directly on your behalf. If that's your setup, you may not need to do anything yourself, but it's worth confirming with your loan servicer rather than assuming, especially in your first year of ownership when the supplemental bill often isn't covered by your existing impound account and may need to be paid separately.

3. Watch for a supplemental bill if you bought or sold a home this year. This bill often arrives separately from your regular tax bill, and it's easy to mistake it for junk mail or a duplicate if you're not expecting it.

4. Pay early if you're mailing a check. Since only a genuine USPS postmark counts, mailing it a few days before the deadline rather than on the deadline itself gives you a real cushion.

5. Set a reminder for April 10 too. The first deadline gets most of the attention, but the second installment carries its own penalty, and it's easy to forget once the holidays are behind you.

None of this is legal or tax advice, and your specific situation, especially if you've recently bought, sold, or are managing an estate or trust property, can change what applies to you. If you're not sure whether a bill you received is your regular tax bill or a supplemental one, or what you actually owe and when, your county tax collector's office is the most reliable place to check, and I'm always happy to help you figure out who to call.

Frequently Asked Questions

When is the property tax deadline in California?

The first installment is due November 1 and becomes delinquent after 5:00 p.m. on December 10. The second installment is due February 1 and becomes delinquent after 5:00 p.m. on April 10. This schedule is set by state law and applies statewide, including both San Mateo and Santa Clara Counties.

What happens if I pay my property tax late?

Missing the December 10 deadline adds a 10% penalty to your first installment. Missing April 10 adds a 10% penalty plus a $40 cost to your second installment. If it remains unpaid into July, additional redemption fees and monthly penalties apply.

What is a supplemental property tax bill?

It's an additional tax bill triggered when a property changes ownership or undergoes new construction. It covers the difference between the home's prior assessed value and its new value, prorated for the months remaining in the fiscal year, and it's billed separately from your regular annual tax bill.

I just bought a home. Will I get two tax bills?

Possibly more than two. You'll get your regular annual bill, and depending on when you closed, you may also get one or two supplemental bills covering the reassessment gap. Watch for a Notification of Supplemental Assessment in the mail roughly 60 days before the actual bill arrives.

Does my mortgage lender pay my property taxes for me?

Only if your loan includes an escrow or impound account for taxes, which many do. Even then, a supplemental bill in your first year of ownership often isn't automatically covered by that account, so it's worth confirming directly with your loan servicer rather than assuming you're covered.

If you're thinking through a move on the Peninsula, whether that's a home valuation, a question about what to expect after a purchase, or figuring out your options as a buyer or seller, I'm happy to walk you through it. Reach out to Kat Bedbury and The Bedbury Group anytime.

About Kat Bedbury and The Bedbury Group Kat Bedbury is a top-producing Peninsula Realtor® with Golden Gate Sotheby's International Realty and co-founder of the Bedbury Group. She helps buyers and sellers throughout San Mateo and Santa Clara Counties navigate real estate with thoughtful strategy, local expertise, and hands-on guidance from preparation through closing.

General guidance only, not legal or tax advice. Deadlines, penalties, and procedures described here reflect San Mateo County Tax Collector and Assessor information as published at smcgov.org as of October 2026; Santa Clara County follows the same state-mandated schedule but administers its own billing separately. Please confirm your specific amounts and due dates directly with your county tax collector or a qualified tax professional.