If your California property tax bill went up this year, the increase almost certainly traces to one of five causes: the automatic annual inflation adjustment built into Proposition 13, a change in ownership that reset your assessed value, new construction on the property, a voter-approved local bond or special assessment added to your bill, or a market recovery that is unwinding a temporary Proposition 8 reduction. Each works differently, and the line items on your bill will usually tell you which one hit you.
The Automatic Two Percent Inflation Bump
Every property’s assessed value can rise each year by the lesser of two percent or the actual change in the California Consumer Price Index.1California Legislative Information. California Revenue and Taxation Code Section 51 No sale, no renovation, no action on your part is needed. This is the quiet reason bills creep up year after year.
When inflation runs below two percent, the smaller figure applies. When it runs higher, the cap holds. A $500,000 base year value becomes $510,000 after one year at the full two percent, which adds about $100 to the base tax. After a decade of two percent increases, that $500,000 base has grown to roughly $609,000.2Santa Clara County Assessor. Understanding Proposition 13 If your bill went up by something close to two percent and nothing else changed, this is almost certainly why.
One thing to confirm while you’re looking at the bill: if the home is your primary residence, the homeowners’ exemption should be knocking $7,000 off the assessed value, worth about $70 a year. You have to file for it. It isn’t automatic.3BOE.ca.gov. Property Tax Savings – Homeowners Exemption
A Sale or Transfer Reset Your Base Year Value
The single biggest reason for a dramatic jump is a change in ownership. When a property sells, the county assessor resets the base year value to the current market price, wiping out whatever Proposition 13 protection had built up.4California State Board of Equalization. Frequently Asked Questions Change in Ownership A home with a protected base of $350,000 that sells for $1.2 million sees its annual base tax jump from $3,500 to $12,000.
A “change in ownership” is broader than a standard sale. It covers most transfers of title or possession where the new party gets the full benefit of the property. Some transfers are statutorily excluded, such as transfers between spouses, but the exclusions are narrow and you have to affirmatively claim them with the county assessor. Assuming a transfer qualifies without filing the paperwork is one of the most expensive mistakes homeowners make.
A Supplemental Bill Showed Up After Closing
If you bought recently, a supplemental tax bill may have arrived three to six months after closing. This bill covers the gap between the prior owner’s assessed value and your purchase price for the remainder of the current fiscal year.5California State Board of Equalization. Supplemental Assessment It’s separate from the regular annual bill and often blindsides buyers who thought escrow handled their first-year taxes.
The math: the assessor subtracts the old assessed value from the new value, applies the tax rate, and prorates based on months remaining in the fiscal year. If you closed in January and the new value is $200,000 higher than the old, you’ll owe one percent on that $200,000 difference for the months through June. It’s a one-time catch-up, not a recurring charge, but it can easily run into thousands of dollars.
You Added Square Footage, an ADU, or Other Improvements
Adding square footage, building an accessory dwelling unit, or making other significant improvements triggers a partial reassessment. The assessor values only the new construction at current market rates and adds that figure to your existing base year value. The original structure and land keep their protected Proposition 13 value.2Santa Clara County Assessor. Understanding Proposition 13
A $200,000 room addition on a home with a $400,000 base year value produces a new total assessed value of $600,000. The $200,000 addition starts fresh with its own base year value and its own two percent annual cap going forward. Cosmetic repairs, routine maintenance, and replacing existing components with equivalent materials generally do not trigger reassessment.
ADUs follow the same rule. Building or converting a structure into an ADU counts as new construction, and the ADU alone is assessed at fair market value and added to your existing assessment. If construction stretches past a year, a partial value gets added each January based on the percentage completed.
One important exception: installing a qualifying solar energy system does not trigger reassessment. That exclusion is set to expire on January 1, 2027, so systems installed through the 2025–26 fiscal year are covered.6California State Board of Equalization. Active Solar Energy System Exclusion Unless the legislature extends it, solar installations after that date will be treated like any other improvement.
A Family Transfer Lost Its Protection Under Proposition 19
If you recently inherited a home from a parent or grandparent, the rules changed in February 2021 and your tax bill may reflect that. Before Proposition 19, parents could pass a home to a child without reassessment regardless of whether the child lived there. Now, the family home can transfer between parents and children (or grandparents and grandchildren) without a full reassessment only if the child actually moves in and uses it as their primary residence.7California State Board of Equalization. Proposition 19 The child must file for the homeowners’ or disabled veterans’ exemption within one year of the transfer.8BOE.ca.gov. Property Tax Savings – Transfers Between Parents and Children
Even when the child moves in, the exclusion has a value cap. The transferred base year value is preserved only up to the existing assessed value plus $1,044,586 for transfers occurring between February 16, 2025 and February 15, 2027.9California State Board of Equalization. BOE Adjusts the Proposition 19 Intergenerational Transfer Exclusion Amount Anything above that combined amount gets added to the assessed value. The base $1 million figure adjusts for inflation every two years.
The exclusion claim must be filed with the county assessor within three years of the transfer (or within six months of a supplemental or escape assessment notice, if later). File late and you only get prospective relief starting the year you submit the claim; the missed years don’t come back.8BOE.ca.gov. Property Tax Savings – Transfers Between Parents and Children And if the child later stops living in the home as a primary residence, the property gets reassessed to current market value as of the following lien date.7California State Board of Equalization. Proposition 19
A New Local Bond or Mello-Roos Charge Appeared
Not every increase traces back to your assessed value. Voter-approved bonds and special assessments sit on top of the one percent Proposition 13 base rate, and they can push your effective rate well above that floor. Scan your bill for line items that aren’t labeled as the general levy.
General obligation bonds issued by cities, counties, and special districts require two-thirds voter approval. School facility bonds need 55 percent approval under Proposition 39 from 2000. The debt service on these bonds is collected through property tax bills.10Legislative Analyst’s Office. Proposition 5 – Allows Local Bonds for Affordable Housing and Public Infrastructure With 55 Percent Voter Approval When your area passes a new measure, the per-parcel cost shows up as a separate line on the next bill.
Mello-Roos Community Facilities District fees are another common addition, especially in newer developments. They fund roads, sewers, water, fire protection, and similar infrastructure within a defined area. Unlike ad valorem taxes, Mello-Roos fees are typically a flat dollar amount per parcel or based on size and use, not market value. A $400,000 home and a $1.2 million home in the same district might pay identical Mello-Roos charges.
Between bonds and special assessments, the combined additions commonly run 0.25 to 0.50 percent of assessed value, though some newer communities with heavy Mello-Roos obligations see total effective rates of 1.5 percent or higher.
The Market Recovered After a Proposition 8 Reduction
If your bill dropped at some point during a market downturn and is now climbing faster than two percent a year, Proposition 8 is likely why. When a property’s market value falls below its Proposition 13 base year value, the county assessor must temporarily lower the assessed value. That reduced figure is sometimes called the “Prop 8 value.”11San Bernardino County Assessor-Recorder-County Clerk. Proposition 8 – Decline in Market Value
Here’s the catch. When the market recovers, the assessor doesn’t have to raise your value gradually at two percent per year. The assessed value can jump by whatever amount the market supports until it reaches the original Proposition 13 base year value, factored up for inflation. A home temporarily reduced from $700,000 to $550,000 might rise to $600,000, then $650,000, then $700,000, with increases of roughly nine percent each year. Only once the assessed value reaches the Proposition 13 base does the two percent cap kick back in.11San Bernardino County Assessor-Recorder-County Clerk. Proposition 8 – Decline in Market Value
The increase isn’t a new tax. It’s the removal of temporary relief. But it rarely feels that way, because the lower bill becomes the baseline in your head.
If You Think the Increase Is Wrong
If none of the above explains your bill, or if a reassessment looks too high, you have two paths.
Informal Review
Most county assessors offer a free informal review, typically open from January 1 through April 30. You submit a form with comparable sales or other evidence that your property is overvalued, and the assessor reviews it internally. A value notice generally arrives in July. There’s no downside: it costs nothing and doesn’t waive your right to a formal appeal.12Orange County Assessor. Request for Informal Assessment Review
Formal Assessment Appeal
If the informal process doesn’t resolve things, file a formal appeal with your county’s Assessment Appeals Board. The standard window runs from July 2 through September 15 in counties where the assessor mails value notices to all taxpayers by August 1. Counties that don’t meet that mailing deadline extend the filing period to November 30.13BOE.ca.gov. County Assessment Appeals Filing Period Miss the window and you wait another year. The formal appeal results in a hearing where you present evidence of value, and the board issues a binding decision.