Property tax in San Ramon starts at California’s 1% base rate applied to your home’s assessed value, with voter-approved school and agency bonds and, in many neighborhoods, Mello-Roos charges layered on top. Contra Costa County handles the assessment, billing, and collection, and the annual bill is split into two installments due December 10 and April 10. Miss either and a 10% penalty attaches the same day.
How Your Bill Is Calculated
Proposition 13, passed in 1978, caps the base property tax rate at 1% of assessed value. Your assessed value starts at what you paid for the home, not what it would sell for today, and the county can raise it by no more than 2% a year regardless of market swings.1California State Board of Equalization. California Property Tax An Overview It only resets to current market value when the property changes hands or you add new construction.
On top of that 1%, your bill carries voter-approved bonds for the San Ramon Valley Unified School District, community college districts, and other local agencies. These vary by what voters have passed over the years, and together they push the effective rate meaningfully above 1% for most San Ramon homeowners.
Mello-Roos and Special Assessments
Many San Ramon neighborhoods sit inside a Community Facilities District, commonly called a Mello-Roos district. These were created under the Mello-Roos Community Facilities Act of 1982 to fund schools, parks, roads, and sewer infrastructure through bonds.2Justia. California Government Code – The Mello-Roos Community Facilities Act of 1982 Mello-Roos charges are not based on your home’s value. They’re fixed amounts tied to the parcel, set when the district was formed, and they show up as separate line items on your tax bill.
Older improvement bonds for street lighting, storm drains, or landscape maintenance can add more. Two homes a block apart can carry different charges, so read your annual bill line by line.
Payment Deadlines and What Happens If You Miss Them
California’s property tax fiscal year runs July 1 through June 30, and the annual bill splits into two installments. The first covers July through December and becomes delinquent at 5:00 p.m. on December 10.3California Legislative Information. California Revenue and Taxation Code 2617 The second covers January through June and becomes delinquent at 5:00 p.m. on April 10.4California Legislative Information. California Revenue and Taxation Code 2618 When either deadline lands on a weekend or holiday, the cutoff moves to the close of the next business day.
A 10% penalty attaches to the unpaid installment the moment you miss the deadline.3California Legislative Information. California Revenue and Taxation Code 2617 On a $5,000 installment, that’s $500 added instantly, with no grace period. If both installments remain unpaid by June 30, the property is declared tax-defaulted as of July 1.
Tax Default and the Five-Year Clock
After default, a redemption penalty of 1.5% per month, or 18% a year, starts accruing on the unpaid balance.5California Legislative Information. California Revenue and Taxation Code 4103 You can still pay off the debt and clear title during the redemption period, but the cost climbs every month you wait.
If the taxes stay unpaid for five years after default, the county tax collector can sell the property at auction.6California Legislative Information. California Revenue and Taxation Code 3691 Nonresidential commercial property can be sold after three years. Contra Costa County holds these tax-defaulted auctions, and once the sale is complete the former owner’s rights are extinguished.
How to Pay
Every parcel in Contra Costa County has an Assessor’s Parcel Number, a ten-digit code in the format 123-456-789-0 printed in the upper left corner of your tax bill.7Contra Costa County. How To Read Your Tax Bill You’ll need it for any payment method. If the paper bill is gone, the Contra Costa County Treasurer-Tax Collector’s website lets you look up your bill by parcel number or street address.
Three payment channels are available:
- By mail to County Tax Collector, PO Box 631, Martinez, CA 94553-0063. The payment counts as timely if the envelope carries a U.S. Postal Service postmark dated on or before the deadline. A private postage meter stamp does not qualify, so take the envelope to a post office counter if you’re close to the deadline.8Contra Costa County. Pay by Mail
- Online through the county portal, which accepts electronic checks and credit or debit cards. Credit and debit card payments carry a service fee from the third-party processor.9Contra Costa County. Pay in Person
- In person at the county office, where cash, personal checks, money orders, cashier’s checks, and certified checks are accepted.9Contra Costa County. Pay in Person
Keep every confirmation number or receipt. Online payments can take a few business days to post, and your proof matters if a processing delay makes the payment look late.
Most homeowners with a mortgage don’t send a check directly. The servicer collects escrow with the monthly mortgage payment and remits to the county. Even so, the tax liability sits on the property, not the lender, so verify through the county portal that your installments were actually received.
Supplemental Bills After You Buy
New owners are often blindsided by supplemental tax bills, which arrive separately from the regular annual bill and look at first like duplicates. When you buy, the assessor recalculates assessed value based on the purchase price and compares it to the value already on the tax roll. You owe tax on the difference for the remaining months of the fiscal year.10California State Board of Equalization. Supplemental Assessment
The timing of your closing determines how many supplemental bills you get. Close between June 1 and December 31 and you’ll receive one supplemental bill for the rest of that fiscal year. Close between January 1 and May 31 and you’ll receive two: one for the remainder of the current fiscal year and another for the full following fiscal year.10California State Board of Equalization. Supplemental Assessment Each has its own due date and its own late penalties. On a San Ramon home that sold well above its prior assessed value, the supplemental bill can run into thousands of dollars, and escrow accounts typically don’t cover it.
Exemptions That Reduce Your Bill
Homeowners’ Exemption
Live in your San Ramon home as your primary residence and the Homeowners’ Exemption cuts $7,000 off your assessed value, saving roughly $70 a year.11California State Board of Equalization. Information Sheet – Homeowners Exemption Small, but worth claiming. You must occupy the home as your principal residence on January 1 and file a one-time claim with the Contra Costa County Assessor. The exemption stays in place until you move out or transfer ownership.12Justia. California Constitution Article XIII Section 3 – Taxation
Disabled Veterans’ Exemption
Veterans with a 100% service-connected disability rating from the U.S. Department of Veterans Affairs qualify for a much larger exemption on their primary residence. The basic version reduces assessed value by roughly $100,000, adjusted annually for inflation, and a low-income version brings that to roughly $150,000 for veterans whose household income falls below a set threshold. A rating below 100% does not qualify, and there are no partial allowances.13California State Board of Equalization. Disabled Veterans Exemption
Proposition 19 Base Year Value Transfer
Homeowners aged 55 or older, people with a severe disability, and victims of a governor-declared wildfire or natural disaster can transfer their existing property’s low assessed value to a replacement primary residence anywhere in California, avoiding the tax jump that would normally follow a move.14California State Board of Equalization. Proposition 19 – Board of Equalization If the replacement home costs the same or less than the original, you keep your old assessed value. If it costs more, the difference between the two sale prices is added to your transferred value. Eligible homeowners can use this up to three times, and the replacement home must be purchased or newly constructed within two years of the original sale.15California State Board of Equalization. Prop 19 Base Year Value Transfer Guidance Questions and Answers
Disputing Your Assessed Value
If you think your assessment is too high, you have two routes. Which one fits depends on whether the market has fallen below your assessed value or whether you believe the number was wrong to begin with.
Proposition 8 Decline-in-Value Review
When current market value drops below your Proposition 13 assessed value, you can ask the assessor for a decline-in-value reduction. It’s an informal process: the assessor looks at comparable sales and lowers your assessed value temporarily to match the market. Once the market recovers, the assessed value climbs back up, still subject to the 2% annual cap.
Formal Assessment Appeal
For a formal challenge, file an application with the Contra Costa County Assessment Appeals Board. The filing window for regular assessments runs July 2 through November 30, and the application fee is $40. For supplemental or escape assessments, you have 60 days from the date of the assessor’s notice.16Contra Costa County. Assessment Appeals Bring comparable sales, documentation of condition issues, or appraisal evidence. The board holds a hearing and can lower, confirm, or raise your assessed value.