The ad valorem tax in California is the property tax counties collect on real estate, and under Proposition 13 it is capped at 1% of a property’s assessed value. Assessed value is set at what you paid for the property, then allowed to rise by no more than 2% per year until a sale or new construction resets it. County assessors handle the valuation, county tax collectors send the bill, and the revenue funds schools, fire departments, and other local agencies.
The Two Rules That Set Your Bill
Nearly everything about California property tax traces back to Proposition 13, the 1978 constitutional amendment that added Article XIII A to the state constitution. It set two limits that still control the math.
The first is a rate cap. The maximum ad valorem tax on any real property is 1% of its full cash value. Anything above 1% on your bill comes from voter-approved bond levies for schools, infrastructure, or other local capital projects. Bonds approved before July 1978 needed only a simple majority; bonds approved afterward generally require a two-thirds vote, though school facility bonds can pass with 55% approval.1California Legislative Information. California Constitution Article XIII A – Tax Limitation
The second limit is on assessed value itself. Instead of taxing property at current market price, Prop 13 locks assessed value to a “base year value,” which is the fair market value at the time of the most recent purchase or completed new construction. That base year value can rise by no more than 2% per year, or by the actual rate of inflation if inflation is lower, producing what the assessor calls the factored base year value.1California Legislative Information. California Constitution Article XIII A – Tax Limitation
The practical effect is that two identical houses on the same block can carry very different tax bills. A home purchased in 1990 might have a factored base year value of $250,000. The house next door, bought last year, could be assessed at $1.2 million. Both owners pay roughly 1% of their own assessed value, but the newer buyer pays nearly five times more.
How the Bill Is Actually Calculated
Start with the base year value: either the original 1975–76 assessed value or the fair market value when the property last changed hands or had new construction completed. Each year, the county assessor increases that figure by the lesser of 2% or the actual change in the California Consumer Price Index. That factored base year value, multiplied by 1%, gives you the ad valorem portion of your bill.
Voter-approved bonds get added on top. In practice, total effective rates in California generally fall between 1.1% and 1.3% of assessed value, depending on which bond measures your community has approved. Each line on your bill represents a separate taxing authority: school districts, community college districts, water districts, and city or county general obligations.
Two different offices handle the process. The county assessor sets your property’s value. The county tax collector produces the bill and collects payment.2Office of the Treasurer-Tax Collector, Riverside County, California. Tax Collector
What Triggers a Reassessment
In normal circumstances, only two things reset your assessed value to current market value: a change in ownership or completed new construction. A kitchen remodel that doesn’t add square footage may trigger a modest reassessment of just the improvement. A sale resets the entire assessed value to the purchase price.1California Legislative Information. California Constitution Article XIII A – Tax Limitation
Parent-Child Transfers Under Proposition 19
Before 2021, parents could transfer real property to their children without a reassessment, regardless of property type or how the child used it. Proposition 19, which took effect in February 2021, narrowed that benefit sharply. A parent-to-child transfer now avoids reassessment only if the child uses the inherited property as a primary residence. Even then, if the property’s current market value exceeds the parent’s factored base year value by more than $1 million, the excess is added to the new assessed value. Investment properties and second homes transferred between parents and children are now fully reassessed.1California Legislative Information. California Constitution Article XIII A – Tax Limitation
Base Year Value Transfers for Seniors, Disabled Homeowners, and Disaster Victims
Proposition 19 also expanded portability. Homeowners who are 55 or older, severely disabled, or victims of a wildfire or natural disaster can transfer their base year value to a replacement home anywhere in California, up to three times in a lifetime. If the replacement home costs more than the original, the difference is added to the transferred base year value. Before Prop 19, this portability was limited to counties that opted in and to a single transfer.
Supplemental Bills After You Buy
New buyers are regularly caught off guard by supplemental tax bills that arrive months after closing. When ownership changes and the property is reassessed, the county issues a supplemental assessment for the difference between the old assessed value and the new one, prorated from the date of the ownership change through the end of the fiscal year on June 30. If you bought mid-year for significantly more than the prior assessed value, you could receive one or two supplemental bills covering the rest of the current fiscal year and, if the purchase happened early enough, the following fiscal year.
Supplemental assessments are separate from your regular annual bill and arrive on their own timeline. Escrow accounts set up by your mortgage lender typically don’t cover them, so budget for them at the time of purchase.
When Market Value Drops Below Assessed Value
If the market falls, you shouldn’t pay taxes on a value your property no longer has. Proposition 8 requires the county assessor to enroll the lower of your factored base year value or your current market value as of the January 1 lien date.3California Board of Equalization. Decline in Value – Proposition 8
This reduction is temporary. The assessor reviews market value every year, and when the market recovers, the assessed value can jump by more than 2% in a single year until it catches back up to the factored base year value. Once it reaches that cap, the normal 2% annual limit resumes. Some counties apply Prop 8 reductions on their own during downturns, but you can also request a review if you believe your property’s market value has fallen below its assessed value.4Riverside County Assessor – County Clerk – Recorder. Decline in Value – Proposition 8
Exemptions and Deferral Programs
Homeowners’ Exemption
The most commonly claimed exemption reduces your property’s assessed value by $7,000 if you own and occupy the home as your principal residence on the January 1 lien date. At the 1% base rate, that saves roughly $70 a year. You apply once through your county assessor’s office and keep it until you move out.5California Board of Equalization. Homeowners’ Exemption
Disabled Veterans’ Exemption
Veterans rated 100% disabled due to a service-connected injury or disease, or their unmarried surviving spouses, qualify for a much larger exemption on their principal residence. It has two tiers: a basic exemption available to all qualifying claimants, and a higher low-income exemption for households below an annual income threshold. Both amounts are adjusted each year for inflation. The basic exemption was $134,706 in 2018 and $161,083 in 2023; current-year amounts are published annually by the Board of Equalization.6California Board of Equalization. Disabled Veterans’ Exemption You can’t claim this exemption and the Homeowners’ Exemption on the same property, but the veterans’ exemption is far more valuable.
Property Tax Postponement
The State Controller’s Property Tax Postponement Program lets qualifying homeowners defer current-year property taxes rather than pay them upfront. You must be at least 62 years old, blind, or disabled; own and live in the home as your principal residence; and have annual household income at or below the program’s threshold (recently $55,181, adjusted periodically). Deferred taxes accrue interest and are secured by a lien on the property, which must be repaid when the home is sold or ownership changes.7California State Controller. Property Tax Postponement
Other Charges Sharing the Bill
Your annual property tax statement will almost certainly include line items beyond the 1% ad valorem levy and bond assessments. These non-ad valorem charges fund specific improvements or services rather than general government operations, and they’re calculated on lot size, frontage, or a flat per-parcel rate instead of property value.
Common examples include lighting and landscaping district fees, flood control assessments, mosquito abatement charges, and Mello-Roos Community Facilities District taxes that fund infrastructure in newer developments. These can add hundreds or thousands of dollars a year, so factor them in when comparing homes.
Property Assessed Clean Energy (PACE) liens may also appear on a tax bill. PACE financing lets owners fund energy efficiency or seismic upgrades through a voluntary assessment collected alongside property taxes, with repayment terms stretching up to 20 years. PACE liens share the same priority as property taxes in a foreclosure, meaning they sit ahead of the mortgage. When the property is sold, the buyer may assume the remaining PACE payments or the seller may need to pay off the balance at closing.8US EPA. Commercial Property Assessed Clean Energy
Payment Deadlines and Late Penalties
Property taxes are paid in two installments. The first covers July through December, is due November 1, and becomes delinquent on December 10. The second covers January through June, is due February 1, and becomes delinquent on April 10. Missing either deadline triggers a 10% penalty on the unpaid amount. If both installments remain unpaid by June 30, additional penalties and costs accrue, and the property eventually becomes tax-defaulted.
Most mortgage lenders collect property taxes through an escrow account as part of your monthly payment and pay the county on your behalf. If you own your home free and clear, or your lender doesn’t escrow, the deadlines are yours to track. County tax collector websites accept online payments, and many offer email reminders when bills are due.
Appealing Your Assessed Value
If you believe your assessed value is too high, whether after a reassessment following a purchase or because comparable sales point to a lower market value, you can file an appeal with your county’s Assessment Appeals Board. The filing window typically opens on July 2 and closes on November 30 for the regular assessment roll. Deadlines for supplemental assessments vary by county, and some use September 15. Most counties charge no filing fee.
The appeals board is an independent panel, separate from the assessor’s office. You’ll need evidence: recent comparable sales, an independent appraisal, or documentation of property defects. If the board agrees, your assessed value is reduced and you receive a refund for any overpayment. Filing an appeal sometimes prompts the assessor’s office to review and informally adjust the value before a hearing.
Where Else Ad Valorem Applies
Real estate dominates the conversation, but the ad valorem concept reaches a few other areas in California. The Vehicle License Fee, calculated as a percentage of a vehicle’s depreciated value, is an ad valorem tax built into your annual registration renewal. Businesses pay ad valorem taxes on certain tangible personal property (equipment, fixtures, and machinery) assessed by the county where the property is located. Those assessments follow similar appeal processes as real property but use separate forms and deadlines.