On a $400,000 purchase in San Mateo County, CA, property tax comes to about $2,308 a year — roughly $192 a month — at this county's effective rate of 0.58%.
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Effective rate 0.58% = this county's median owner-occupied tax bill ($8,637, ACS 2022 5-year estimate) divided by the typical home value at the time ($1,496,279, Zillow, 2022-12-31). Exemptions the seller holds — homestead, senior, veteran — usually do not transfer with the deed, so a new purchase can run above this figure. The county assessor sets the assessed value; this is an estimate, not a quote.
If you pay late
A 10% penalty is added the day after the December 10 deadline, and 10% plus a $40 cost after the April deadline.
Fiscal year July 1 to June 30; the Treasurer-Tax Collector mails secured bills in October. If a due date lands on a weekend or public holiday, most counties move it to the next business day — check the county's own notice before relying on the shift.
How to pay
Online: through county-taxes.net — the only portal this county operates.
By post: mail a cheque to the treasurer's office; the postmark date usually counts, not the arrival date.
In person: the treasurer's office during business hours; bring your bill or parcel number.
Mortgage escrow: if your taxes are escrowed, the servicer pays — you still owe the difference if your escrow is short.
Common questions
When are property taxes due in San Mateo County, CA?
1st installment: November 1, 2026. 2nd installment: February 1, 2027.
What happens if I pay late in San Mateo County?
A 10% penalty is added the day after the December 10 deadline, and 10% plus a $40 cost after the April deadline.
How do I pay San Mateo County property tax?
Pay online through county-taxes.net, the county's own payment portal, or by post or in person at the treasurer's office.
Is the San Mateo County deadline the same every year?
Fiscal year July 1 to June 30; the Treasurer-Tax Collector mails secured bills in October. Counties shift dates when billing is delayed, so confirm against the county source linked on this page.
How much is property tax on a $400,000 house in San Mateo County, CA?
About $2,308 a year, or $192 a month, at this county's effective rate of 0.58%. That rate is the county's median owner-occupied tax bill ($8,637) divided by the typical home value ($1,496,279). A seller's homestead or senior exemption usually does not transfer, so a new purchase can cost more.
What if I can't pay in full?
Most counties offer instalment plans or partial payment — ask the treasurer before the due date, not after. Once the bill is delinquent the options shrink and the fees start.
Does a late payment affect my mortgage?
Unpaid property tax is a lien on the property in most states, which your servicer may pay and then bill you for, with fees. It does not disappear.
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CountyTaxDates is an independent reference and is not a government agency. Deadlines change and exceptions apply — always confirm with your county treasurer using the official link on this page. Nothing here is tax, legal or financial advice.