The property tax rate in San Mateo County starts at a 1% base set by the California Constitution, and most homeowners end up paying somewhere between 1.1% and 1.3% of assessed value once voter-approved bond repayments and special district charges are added in. The exact figure depends on which tax rate area your property sits in. What you actually owe each year is that rate multiplied by the assessed value the county assigns to your property, and both pieces are worth understanding before you budget around a bill.
Why Most Bills Run Above 1%
Article XIII A of the California Constitution, enacted through Proposition 13 in 1978, caps the general ad valorem property tax at 1% of a property’s full cash value.1California Legislative Information. California Constitution – Article XIII A – Tax Limitation No county, city, or school district can lift that base rate on its own. On your bill, this portion shows up as the “1% General Tax Levy” and is usually the largest line item. The county collects it and then distributes it among schools, the county general fund, cities, and special districts under formulas set in state law.
The reason your total runs higher is Revenue and Taxation Code Section 93, which lets local agencies collect what they need to cover principal and interest on general obligation bonds that voters authorized, either before July 1, 1978, or by a two-thirds vote after that date.2California Legislative Information. California Code Revenue and Taxation Code 93 – Levy of Ad Valorem Property Tax These bond levies rise and fall year to year as debt is issued and retired, so the non-base portion of your bill can shift even when your assessed value doesn’t.
Some properties also carry Mello-Roos special taxes. Under the Mello-Roos Community Facilities Act of 1982, a community facilities district can impose a special tax on properties within its boundaries to fund infrastructure, schools, parks, fire protection, and similar services. Mello-Roos charges aren’t tied to assessed value; they follow a formula fixed when the district was created and approved by a two-thirds vote. Look under “Special Assessments” or “Direct Charges” on your annual bill to spot them.
How Assessed Value Is Set
The rate matters less than what it’s being applied to. When you buy a property, the San Mateo County Assessor establishes a “base year value” equal to the property’s fair market value at the time of purchase.1California Legislative Information. California Constitution – Article XIII A – Tax Limitation From then on, the taxable value can rise annually by no more than 2% or the change in the California Consumer Price Index, whichever is lower.3California Legislative Information. California Revenue and Taxation Code 51 In years when inflation runs below 2%, the increase is smaller.
That cap is why two identical homes next door to each other can carry very different tax bills. The longer you’ve owned, the further your assessed value has drifted below current market value, and a new buyer takes on a bill set from today’s price.
What Resets Your Assessment
Two events reset assessed value to current market value: a change in ownership and completion of new construction. A sale is the obvious case, but a change in ownership can also include transfers into certain trusts, adding or removing someone from a deed, and some corporate restructurings. The Assessor’s office decides whether a particular transfer qualifies.
New construction isn’t limited to building from scratch. Under Revenue and Taxation Code Section 70, it covers additions that increase square footage, major renovations that effectively create a new structure, and conversions to a different use, such as turning a garage into living space or splitting a single-family home into multiple units.4California State Board of Equalization. New Construction Only the value added by the new work gets reassessed, not the whole property. Add a deck to a home carrying a long-held low base year value and the Assessor layers the deck’s value on top of your existing assessment.
Routine maintenance and repairs don’t trigger a reassessment. Repainting, replacing carpet, or swapping in a comparable water heater is safe.4California State Board of Equalization. New Construction Kitchen and bathroom remodels sit in a gray zone: like-for-like fixture replacements generally stay on the maintenance side, while upgraded finishes, floor plan changes, or expanded footprints cross into assessable territory.
Supplemental Bills After You Buy
New buyers often get caught off guard by supplemental tax bills that arrive separately from the regular annual bill. When a property changes hands or new construction is completed, the Assessor calculates the difference between the old assessed value and the new market value, then prorates it over the months remaining in the fiscal year, which runs July 1 through June 30.5California State Board of Equalization. Supplemental Assessment
When you close determines how many supplemental bills you’ll see. Close between January 1 and May 31 and you can expect two bills, one covering the remainder of the current fiscal year and a second covering the entire next fiscal year.6San Mateo County Clerk. Property Tax Bills and Refunds Close between June 1 and December 31 and you’ll typically see one. These are separate obligations. They don’t credit or reduce the regular annual bill, which still has to be paid in full on its usual schedule.
Exemptions That Lower the Number Being Taxed
If you live in your San Mateo County home as your primary residence on January 1, you can claim the homeowners’ exemption, which reduces your assessed value by $7,000.7California Legislative Information. California Code Revenue and Taxation Code – RTC 218 – Homeowners Property Tax Exemption At a 1.1% effective rate, that’s roughly $77 a year. Small, but it’s free money otherwise left behind. File form BOE-266 once with the San Mateo County Assessor and the exemption stays in place as long as you continue to occupy the home.8California State Board of Equalization. Homeowners’ Exemption
Veterans who are totally disabled from a service-connected injury or disease, or who are blind in both eyes or have lost the use of two or more limbs, qualify for a much larger exemption on their primary residence under Revenue and Taxation Code Section 205.5.9California Legislative Information. California Revenue and Taxation Code 205.5 For 2026, the basic exemption is approximately $180,671 off full value, and veterans whose household income falls below the adjusted threshold can receive approximately $271,009. Unmarried surviving spouses of eligible deceased veterans may also qualify.
Pushing Back When the Assessment Looks Too High
If current market value has dropped below your factored base year value, you can request a temporary reduction, sometimes called a Proposition 8 reduction. Revenue and Taxation Code Section 51(a)(2) requires the Assessor to enroll the lower of the factored base year value or current market value each year.3California Legislative Information. California Revenue and Taxation Code 51 You’ll need comparable sales data, ideally recent transactions for similar properties as close to the January 1 lien date as possible. The reduction is temporary. As the market recovers, the Assessor can increase the enrolled value back up by more than 2% in a year until it reaches the factored base year value, at which point the usual 2% cap resumes.
For a formal challenge to the Assessor’s valuation, file an appeal with the San Mateo County Assessment Appeals Board. For the 2026 assessment year, the window runs from July 2, 2026, through November 30, 2026.10San Mateo County Clerk. Property Tax Relief – Assessor Miss it and you forfeit your right to contest that year’s assessment. The strongest evidence is recent comparable sales from your neighborhood, ideally within a few months of the January 1 lien date; an independent appraisal also carries weight. Before filing, call the Assessor’s office. Informal conversations sometimes resolve valuation disagreements without a hearing, and the staff can walk you through how your value was determined.
When Payment Is Due
San Mateo County splits the annual bill into two installments:11County of San Mateo. Secured Property Taxes
- First installment: due November 1, with a grace period through 5:00 p.m. on December 10. After that, a 10% penalty is added.
- Second installment: due February 1, with a grace period through 5:00 p.m. on April 10. Missing this deadline triggers a 10% penalty plus a $40 cost.
You can pay through the San Mateo County Tax Collector’s website by electronic check or credit card, by phone, by mail, or in person at the county government center.12County of San Mateo. Tax Collector Credit card and PayPal payments carry a service fee, so electronic check is the cheapest online option. If December 10 or April 10 falls on a weekend or holiday, the deadline extends to the next business day.
Finding Your Exact Rate
Because voter-approved bonds and special assessments vary by location, two homes on opposite sides of San Mateo County can carry meaningfully different total rates. The county’s Assessor-Clerk-Recorder provides an online property tax lookup tool where you can search by address or parcel number and see every line item on the current bill.13San Mateo County Clerk. Property Tax Look-up – Assessor If you’re shopping for a home and want to estimate what you’ll owe, pull the current bill for the property, note the total rate, and apply it to your expected purchase price rather than the seller’s assessed value, since the assessment will reset to the price you pay.