How to Calculate Property Tax in California: Rates, Exemptions, Example

To calculate property tax in California, multiply your home’s assessed value by your local combined tax rate (which starts at 1% and climbs with voter-approved bonds), then add any flat-dollar charges like Mello-Roos. The assessed value is usually what you paid for the property, adjusted upward each year by an inflation factor capped at 2%. Exemptions you qualify for come off the assessed value before you multiply. Everything else is detail.

Here is the full calculation in four steps.

Step 1: Find Your Assessed Value

Your assessed value starts with a “base year value,” which is the property’s fair market value on the day you bought it, or the day it was last reassessed after a change in ownership or new construction. Each year after that, the county assessor increases the base year value by an inflation factor tied to the California Consumer Price Index. The increase can never exceed 2%, even if actual inflation runs higher.¹ In low-inflation years the increase can be well under 2%, because the factor tracks the actual CPI change rounded to the nearest thousandth of a percent.² The result is called your “factored base year value,” and it is the number the tax calculation starts from.

You can look it up on your county assessor’s website by searching your Assessor’s Parcel Number or street address. Your most recent tax bill lists it too. If you have owned the home for many years, this number is often well below what the property would sell for today.

If the Market Drops Below Your Assessed Value

If current market value falls below your factored base year value, the assessor is required to temporarily lower your assessment to match the market value. This is known as a “Proposition 8” reduction.³ The assessor reviews these values each year, and if the market recovers, the assessed value can rise back up, but never higher than the original factored base year value. You should not need to file anything; the reduction is supposed to be applied automatically.

If You Added a Room, Pool, or Other Improvement

Major improvements are reassessed, but only the new portion. The assessor estimates the market value the improvement added and tacks that amount onto your existing assessed value as a separate base year value for the new work.⁴ The original base year value for the rest of the property is unchanged. If your home is assessed at $400,000 and you add a room the assessor values at $50,000, your new total assessed value is $450,000, and each piece grows independently under the 2% cap after that.

A sale or other change in ownership is different: the whole property resets to current fair market value, and the new owner’s assessed value becomes the purchase price (or fair market value if there was no arm’s-length sale).⁵ The annual inflation factor runs from that new base.

Step 2: Subtract Any Exemptions

Exemptions reduce the assessed value before you apply the tax rate, so a $7,000 exemption at a 1% rate saves about $70 a year.

The homeowners’ exemption is $7,000 off assessed value if you own and live in the home as your primary residence. It does not apply to rental properties, vacation homes, vacant properties, or homes under construction on the lien date (January 1).⁶ File form BOE-266 once with your county assessor and the exemption stays active as long as you live there.⁷

The disabled veterans’ exemption is much larger. For the 2026 lien date, the basic exemption reduces assessed value by $180,671. Veterans with household income of $81,131 or less qualify for the low-income version, which reduces assessed value by $271,009.⁸ It is available to veterans with a service-connected disability or their unmarried surviving spouses. You cannot claim both the homeowners’ exemption and the disabled veterans’ exemption on the same property; the veterans’ exemption replaces it.⁶

Installing a qualifying active solar energy system, such as rooftop panels or a solar water heater, does not raise your assessed value. The assessor excludes the system’s value from any new construction assessment.⁹ Solar pool heaters and hot tub heaters do not qualify.

Step 3: Find Your Combined Tax Rate

Article XIII A of the California Constitution caps the base property tax rate at 1% of assessed value statewide.¹⁰ That part is the same for every property owner in California. Where properties differ is in the voter-approved add-ons stacked on top: school construction bonds, community college bonds, water district improvements, and similar levies. Each is calculated as a percentage of assessed value, and the mix varies by neighborhood.

Every parcel is assigned to a Tax Rate Area, a geographic zone that bundles all the applicable levies into one combined rate. You can find your Tax Rate Area and the itemized rates that make it up on your county auditor-controller’s website. A typical combined rate falls somewhere a bit above 1%, but the exact figure depends on which bonds have passed where you live.

Multiply your net assessed value from Step 2 by this combined rate. That gives you the ad valorem portion of your bill — the part that scales with your property’s value.

Step 4: Add Flat-Dollar Charges

Many parcels carry fixed charges that do not depend on assessed value. The most common are special taxes under the Mello-Roos Community Facilities Act of 1982, which lets newly developed areas fund infrastructure through special taxes levied on each parcel.¹¹ Mello-Roos charges appear as separate line items on your tax bill and typically fund things like road maintenance, fire protection, or landscaping in your development. Other direct assessments (sewer, lighting, vector control) work the same way.

Pull these amounts from your parcel’s record on the county auditor-controller’s website and add them to the ad valorem total. That is your annual property tax.

A Worked Example

Say you bought a home for $500,000 three years ago, you live in it, and your Tax Rate Area has a combined ad valorem rate of 1.2% with $800 a year in Mello-Roos.

Factored base year value after three 2% adjustments: roughly $530,600.
Subtract the $7,000 homeowners’ exemption: net taxable value of $523,600.
Multiply by 1.2%: $6,283.
Add $800 in Mello-Roos: $7,083 for the year.

Swap in your own numbers from the assessor’s office (for assessed value) and the auditor-controller (for your Tax Rate Area and direct assessments) to run this on your parcel.

If You Just Bought or Built: Expect a Supplemental Bill

The calculation above produces your ongoing annual bill. New owners and anyone who just finished construction also face a one-time supplemental bill that trips up a lot of first-time California buyers.

Here is why. When you buy a home or complete construction partway through the fiscal year (July 1 through June 30), the regular tax bill still reflects the previous owner’s assessed value. The county issues a separate supplemental bill to capture the difference between the old and new assessed values for the months remaining in that fiscal year. It usually arrives within six months of closing or completion.¹²

The amount is prorated by month. The assessor takes the net supplemental assessment (new value minus old value), multiplies it by the tax rate, and then multiplies by a proration factor based on how many months are left in the fiscal year.¹³ Close in October and nine months remain, so the factor is 0.75; a $200 annual increase becomes a $150 supplemental charge.

If the change happens between January 1 and May 31, you will get two supplemental bills: one for the current fiscal year and one covering the next full year, because the new assessed value will not hit the regular roll until the year after that.¹² Budget for it when you plan a purchase.

If Your Assessment Looks Too High

If the assessed value the county is using looks higher than what your home would actually sell for, you can challenge it. File a formal appeal with your county’s Assessment Appeals Board. The annual filing window generally opens on July 2 and closes either September 15 or November 30, depending on whether your county’s assessor mailed assessment notices by August 1.¹⁴ Check your county’s specific deadline each year.

The strongest evidence for a residential appeal is recent comparable sales: homes similar to yours that sold near the January 1 lien date for less than your assessed value. The board can also consider an independent appraisal, a cost approach (what it would take to rebuild), or an income approach for a rental.¹⁴ Sales that closed more than 90 days after the lien date cannot be used. If the board agrees, the lower value takes effect for that tax year and carries forward until the next reassessment event.

1
Justia. California Constitution Article XIII A Section 2
2
California Legislative Information. California Revenue and Taxation Code Section 51
3
California State Board of Equalization. Decline in Value – Proposition 8
4
California State Board of Equalization. New Construction
5
California State Board of Equalization. Change in Ownership – Frequently Asked Questions
6
California Legislative Information. California Revenue and Taxation Code Section 218
7
California State Board of Equalization. Homeowners’ Exemption
8
State Board of Equalization. Disabled Veterans’ Exemption Increases for 2026
9
California State Board of Equalization. Active Solar Energy System Exclusion – Frequently Asked Questions
10
Justia. California Constitution Article XIII A Section 1 – Tax Limitation
11
California Legislative Information. California Government Code Section 53311
12
Riverside County Assessor-County Clerk-Recorder. Supplemental Tax Bills
13
OC Treasurer-Tax Collector. Computation of Supplemental Taxes
14
California State Board of Equalization. Assessment Appeals Frequently Asked Questions