San Mateo County mails secured property tax bills by November 1. The first installment’s penalty starts after 5:00 p.m. on Thursday, December 10, 2026. If you pay by mail, your envelope needs a United States Postal Service postmark on or before that date.
The dates on the bill decide when a payment is on time. They also decide when a 10% penalty applies. Here is the full calendar from the San Mateo County Tax Collector and the California State Board of Equalization. It includes one exemption and one form worth knowing about.
The two installment dates
The county’s fiscal year begins on July 1 and ends on June 30. The secured tax bill is payable in two installments.
The first installment is due on November 1. The county gives you until 5:00 p.m. on December 10 to pay before a 10% penalty is added to your bill.
The second installment is due on February 1. Its grace period expires at 5:00 p.m. on April 10. If the installment is still unpaid then, the county adds a 10% penalty and a $40.00 cost.
A delinquent date can fall on a weekend or holiday. In that case the penalty is not imposed until 5:00 p.m. on the next business day. April 10, 2027 is a Saturday. Under that rule the second installment’s penalty would begin after 5:00 p.m. on Monday, April 12. Confirm the exact date on the county’s page when the time comes.
The postmark rule and how to pay
You can mail your payment. Your envelope must carry a United States Postal Service postmark on or before the delinquent date. California law requires the Tax Collector to accept the postmark, not a private meter date, as the date of payment. A date printed by a private postage meter doesn’t count.
Mailed payments go to the San Mateo County Tax Collector, PO Box 45878, San Francisco, CA 94145-0878. Checks are made payable to the San Mateo County Tax Collector. You can also pay in person at 555 County Center, First Floor, Redwood City. Hours are Monday through Friday, 9 a.m. to 5 p.m., excluding holidays.
The county accepts Visa, MasterCard, Discover and American Express by phone or on its website. Card payments carry a 2.35% service fee. The county says the Treasurer-Tax Collector does not retain that fee. Its page also notes that you can now pay annual secured property taxes monthly through its site.
The homeowners’ exemption
California provides a $7,000 reduction in the taxable value of a qualifying owner-occupied home. The home must have been your principal place of residence on the lien date, January 1.
You claim the exemption with a one-time filing with the county assessor. The form is BOE-266, and the assessor provides it. A first-time filer can file any time after becoming eligible. The Board of Equalization says to file no later than February 15 to receive the full exemption for that year. The Board’s page doesn’t address renewal, so ask the assessor if you’re unsure.
Claimants are also responsible for notifying the assessor when they are no longer eligible. The Board says December 10 is the last day to terminate the exemption without penalty. The assessor should receive notice by that date.
One form to know about after a purchase
A recorded deed must be accompanied by a Preliminary Change of Ownership Report at the time of recording. If the report isn’t filed then, the county recorder may charge an additional $20 recording fee. The San Mateo page on this site covers the city itself.
Sometimes a transfer is not recorded, or no report was filed at recording. In that case the owner files a Change in Ownership Statement, Form BOE-502-AH, within 90 days of the date of transfer. A penalty is triggered only when the county assessor asks for that statement and it isn’t filed.
If you inherited a home, the Prop 19 article covers the separate reassessment rules. The seller net sheet guide walks through the other costs of a sale.
Frequently asked questions
Q: When is the San Mateo County property tax deadline?
The first installment is due November 1 and becomes delinquent after 5:00 p.m. on December 10. The second is due February 1 and becomes delinquent after 5:00 p.m. on April 10.
Q: What happens if I pay after December 10?
A 10% penalty is added to the first installment.
Q: Does a postmark count as the payment date?
Yes, if it is a United States Postal Service postmark on or before the delinquent date. The county doesn’t accept a private meter date.
Q: How much is the homeowners’ exemption, and when do I file?
It is a $7,000 reduction in taxable value for a principal residence on January 1. Claim it on Form BOE-266 with the county assessor, no later than February 15 for the full exemption that year.
Q: Do I need to file anything with the county after buying a home?
A Preliminary Change of Ownership Report goes in with the recorded deed. If none was filed at recording, a Change in Ownership Statement is due within 90 days of the date of transfer.
Which date goes with what
December 10 applies to the first installment and to ending a homeowners’ exemption without penalty. February 15 is the filing date for a full-year exemption. April 10 applies to the second installment, which in 2027 means 5:00 p.m. on Monday, April 12.
The county and the Board publish these dates on separate pages, so it is easy to mix them up. December 10 is a payment deadline with a 10% penalty. February 15 is a filing date for the exemption, with no payment attached. Check the date against what you are doing before you rely on it.
If you’re closing a purchase or sale this winter, I’m happy to go through which of these dates fall around your closing.
Sources: San Mateo County Tax Collector, Secured Property Taxes (smcgov.org/tax/secured-property-taxes). California State Board of Equalization, Homeowners’ Exemption (boe.ca.gov/proptaxes/homeowners_exemption.htm) and Change in Ownership FAQ (boe.ca.gov/proptaxes/faqs/changeinownership.htm). All read November 2, 2026. Dates and fees can change, so confirm on the county’s page before you pay.
About the author:
Mark Tauber sells homes on the San Francisco Peninsula, working across San Mateo, Burlingame, Hillsborough, Belmont, San Carlos, Millbrae, Redwood City, and the coast. More at marktauber.com.
