San Mateo County property tax bills start with California’s 1% constitutional base rate applied to your assessed value, then add voter-approved bonds and special district charges that push the effective rate higher depending on where the property sits. For most homeowners, the total lands somewhere between 1.05% and 1.20% of assessed value. The revenue funds schools, fire and police, roads, parks, and public health across the county, and the exact figure on your bill reflects your location, when you bought, and which exemptions you claim.
How Your Bill Is Calculated
Article XIII A of the California Constitution caps the general ad valorem property tax at 1% of a property’s full cash value.1Justia. California Constitution Article XIII A – Tax Limitation The county collects that 1% and distributes it to cities, school districts, and special districts under a state formula.
On top of the base, your bill picks up voter-approved bonds and special assessments: school construction bonds, city infrastructure, flood control, mosquito abatement, and similar district-level charges.2San Mateo County Assessor-County Clerk-Recorder & Elections. Office of the Assessor Every parcel sits in a Tax Rate Area, a geographic zone defined by the unique combination of taxing districts that overlap at that location.3California Department of Tax and Fee Administration. Tax Area Services Section Two homes with identical assessed values in different parts of the county can owe different totals. The Assessor’s website lets you look up your parcel and see the specific levies that apply.
How Your Assessed Value Is Set
The rate is only half the equation. Assessed value drives the dollar amount, and Proposition 13 has governed how that value moves since 1978. When you buy a property or finish new construction, the assessor sets a base year value equal to the full cash value at that moment.4Justia. California Constitution Article XIII A – Tax Limitation – Section 2 That number becomes the starting point for every future bill.
From there, annual increases are capped at 2% or the rate of inflation, whichever is lower.4Justia. California Constitution Article XIII A – Tax Limitation – Section 2 If neighborhood values jump 15% in a year, your assessed value still rises by no more than 2%. That is why long-term owners in San Mateo County often pay on an assessed value well below current market.
When Values Drop
The system also adjusts downward. Under Proposition 8, the assessor must use the lower of your factored base year value or the property’s fair market value as of January 1. If the market falls below your Prop 13 base, your taxes fall with it. When the market recovers, though, the assessor can raise your value back up by more than 2% per year until it reaches your factored base year value again. San Mateo County accepts informal decline-in-value requests through October 31 for the current assessment year.5San Mateo County Assessor-County Clerk-Recorder & Elections. Property Tax Relief
Mello-Roos Charges
Some parcels carry a Mello-Roos special tax that is not part of the standard rate. Created under the Mello-Roos Community Facilities Act of 1982, these taxes fund infrastructure like streets, water systems, sewers, schools, and parks within designated districts. The charge is not based on assessed value. It is typically calculated from lot size, building square footage, or number of bedrooms.
If your property sits inside a Community Facilities District, the Mello-Roos line appears separately on your annual bill and can add hundreds or thousands of dollars. These assessments are most common in newer developments where the district paid for the subdivision’s infrastructure. Sellers must disclose Mello-Roos obligations, so ask specifically about them before closing.
Supplemental Bills After Buying or Building
Expect a supplemental tax bill in the mail after a purchase or completed construction. The assessor recalculates the base year value immediately rather than waiting for the next regular cycle.6California Legislative Information. California Code Revenue and Taxation Code RTC 75.11 The supplemental bill covers the difference between the old and new assessed values, prorated for the portion of the fiscal year remaining after the triggering event.
You may receive one or two of these. If ownership changes or construction finishes between January 1 and May 31, the assessor issues two supplemental assessments, covering both the current fiscal year and the upcoming one.6California Legislative Information. California Code Revenue and Taxation Code RTC 75.11 Events between June 1 and December 31 generate a single supplemental bill. Routine maintenance and cosmetic repairs do not trigger supplemental assessments, and most transfers between spouses are excluded.
Exemptions and Relief Programs
Homeowners’ Exemption
If the home is your primary residence, you qualify for a $7,000 reduction in assessed value under Revenue and Taxation Code Section 218.7California Legislative Information. California Code RTC 218 – Homeowners Property Tax Exemption At a combined rate near 1.1%, that saves about $77 a year. It does not apply to rentals, vacation homes, or properties under construction on the lien date. File once with the assessor’s office and the exemption stays in effect until you sell or move out.
Disabled Veterans’ Exemption
Veterans rated 100% disabled from a service-connected condition, or compensated at the 100% rate for unemployability, qualify for a far larger exemption on their primary residence.8California Department of Tax and Fee Administration. Disabled Veterans Exemption The basic exemption for 2026 is $180,671. Veterans with household income below $81,131 qualify for the low-income exemption of $271,009. Both figures adjust annually with inflation. Unmarried surviving spouses of qualifying veterans may also claim this exemption.
Property Tax Postponement
California’s Property Tax Postponement Program lets qualifying homeowners defer current-year taxes on a primary residence. You must be a senior, blind, or disabled, with annual household income of $55,181 or less. The state effectively lends you the tax payment; the deferred amount accrues interest and becomes a lien repayable when you sell, move out, or pass away. The 2025–26 filing period closes February 10, 2026.9California State Controller. Property Tax Postponement
Proposition 19 Transfers
Proposition 19, effective in 2021, changed two things: it expanded base-year transfer rights for certain owners and tightened the rules on inherited property.
Transfers for Seniors, Disabled Persons, and Disaster Victims
Owners who are 55 or older, severely disabled, or victims of a wildfire or governor-declared natural disaster can transfer their current tax base to a replacement primary residence anywhere in California. The replacement must be purchased or newly built within two years of selling the original, and seniors and disabled owners can use the benefit up to three times.10California Legislative Information. California Revenue and Taxation Code 69.6
If the replacement costs the same or less than the original’s market value, your old base carries over unchanged. “Equal or lesser value” means 100% of the original’s sale price if you buy the replacement first, 105% within the first year after selling, and 110% in the second year.11California State Board of Equalization. Proposition 19 If the replacement costs more, the excess value gets added to your transferred base.
Parent-Child and Grandparent-Grandchild Transfers
Prop 19 narrowed the inheritance exclusion sharply. Before 2021, children could inherit a parent’s low Prop 13 base on any property, including rentals and commercial real estate, with up to $1 million in additional value excluded. Now the exclusion applies only when the property was the parent’s primary residence and the child makes it their own primary residence within one year of the transfer.12California Legislative Information. California Revenue and Taxation Code 63.2 Family farms also remain eligible.
Even when the exclusion applies, there is a cap. The transferred value is limited to the existing assessed value plus $1,044,586 (the biennially adjusted figure for transfers through February 15, 2027).11California State Board of Equalization. Proposition 19 Any value above that is reassessed at market. The child must file for the homeowners’ exemption within one year and submit the exclusion claim within three years.12California Legislative Information. California Revenue and Taxation Code 63.2 Grandparent-to-grandchild transfers qualify only when the grandchild’s parent (the grandparent’s child) is deceased at the time of transfer.
Payment Deadlines and Methods
San Mateo County bills come in two installments. The first is due November 1 and delinquent after 5 p.m. on December 10. The second is due February 1 and delinquent after 5 p.m. on April 10.13Taxes. Property Tax Function Important Dates You can pay both together with the first installment if you prefer.
E-checks drawn on a checking or savings account carry no fee. Credit cards work but add a 2.35% convenience fee charged by the processor, and debit cards cost a flat $3.95.14County of San Mateo. Payment Options On a $10,000 bill, paying by credit card adds about $235, which makes the e-check option considerably cheaper.
If you mail a check, the USPS postmark is your official payment date.15California Legislative Information. California Code RTC 2512 – Medium of Payment Be careful with metered postage from home or office machines; the county may not accept a meter stamp as a valid postmark, and a late arrival means a penalty.16County of San Mateo. Postmark Details You can also pay in person at the Tax Collector’s office at 555 County Center, Floor 1, Redwood City, which has an after-hours drop box for checks, cashier’s checks, and money orders.17County of San Mateo. Tax Collectors Office Main Office
Late Penalties, Default, and Tax Sales
Missing December 10 or April 10 triggers an immediate 10% penalty on the delinquent installment.18California Legislative Information. California Code Revenue and Taxation Code RTC 2617 The second installment also adds a $40 administrative cost on top of the 10%.16County of San Mateo. Postmark Details On a $5,000 installment, that is $500 in penalties for being one day late. No grace period, no exceptions.
If taxes stay unpaid through June 30, the property is declared tax-defaulted. A $15 redemption fee is added and interest begins accruing at 1.5% per month on the unpaid balance.19California Legislative Information. California Code Revenue and Taxation Code RTC 4103 That rate compounds quickly: a year in default means 18% in accumulated interest on top of the original 10% penalty.
Residential property in default for five or more years without redemption becomes eligible for sale at auction to recover the unpaid taxes.20Justia. California Revenue and Taxation Code 3691-3731.1 Nonresidential commercial property faces a three-year timeline. Once a property reaches “power to sell” status, installment plans are off the table. The only way to stop the sale is to pay all delinquent taxes, penalties, interest, and fees in full before the auction date.
Appealing Your Assessment
If you think the assessed value is too high, you can challenge it through an informal review or a formal appeal.
Informal Review
Start with the Assessor’s Decline in Assessed Value Program. Submit an informal application arguing that market value has fallen below the current assessed value. The deadline is October 31 for the current assessment year.5San Mateo County Assessor-County Clerk-Recorder & Elections. Property Tax Relief If the assessor agrees, your value is reduced without a hearing. If the assessor disagrees or you have no answer by mid-November, protect yourself by filing a formal appeal before November 30.
Formal Appeal
File a written application with the San Mateo County Assessment Appeals Board between July 2 and November 30.21County of San Mateo. About Assessment Appeals State law normally runs the window from July 2 through September 15, but counties where the assessor does not provide value notices by August 1 get the November 30 deadline.22California Legislative Information. California Revenue and Taxation Code 1603 Each application carries a $30 nonrefundable filing fee.
Your application must state the facts supporting a reduction and your opinion of the property’s full value.22California Legislative Information. California Revenue and Taxation Code 1603 Bring comparable sales, photos of condition issues, or an independent appraisal to the hearing. For supplemental or escape assessments, the window is different: 60 days from the date printed on the assessment notice.21County of San Mateo. About Assessment Appeals Keep paying the bill in full while the appeal is pending; any overpayment is refunded if the board rules for you.