How to Challenge Your California Property Tax Assessment If You Think It's Too High
For most California homeowners, property tax is the single largest recurring cost of ownership after the mortgage payment itself. If you believe your county assessor assigned your home a value that's higher than it should be, you have the legal right to appeal - and in most counties, the window to do so for the current tax year is open right now, through November 30.
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How Your Assessed Value Gets Set
California's property tax system runs on rules established by Proposition 13, the 1978 ballot measure that fundamentally changed how the state taxes real property. When you buy a home, the assessor establishes a "base year value" equal to the purchase price. From that point forward, annual increases are capped at 2% or California's inflation rate, whichever is lower - regardless of what the housing market does. The general tax rate is 1% of assessed value, plus any voter-approved local bonds and special assessments, which is why two neighbors with nearly identical homes can carry very different tax bills if one bought in 1998 and the other bought last year.
The assessor's office resets assessed value to current market value when property changes hands or undergoes new construction. The valuation date that controls any given tax year is January 1 - so for the 2026-27 tax year, the assessor is working from a snapshot of your property's value and condition as of January 1, 2026.
Two Situations That Can Give You Grounds to Appeal
The most common basis for an appeal is a decline in market value. Under what's known as the Prop 8 adjustment - a separate 1978 measure - if your home's fair market value has dropped below its Prop 13 assessed value, you can ask the county to temporarily reduce the taxable value to match. The relevant comparison is your property's market value as of January 1 of the tax year you're appealing, not current market conditions. This kind of appeal tends to pick up during local market corrections, when assessed values set during a peak period end up higher than what comparable homes are actually selling for.
The other basis is an error in the base year value itself - meaning the assessor assigned the wrong starting number when the property last changed hands or was newly built. This can happen if the assessor relied on flawed comparable sales, used incorrect square footage or lot dimensions, or misidentified the property's condition or features. Factual errors in the assessor's records, like a wrong bedroom count, can independently inflate a taxable value and are worth checking against the assessor's property detail page, which is publicly searchable in most counties.
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How to File an Assessment Appeal
Appeals go to your county's Assessment Appeals Board - not the assessor's office directly, though contacting the assessor first for an informal review is often a practical first step, particularly when the concern is a straightforward factual error. That informal review doesn't replace a formal appeal and doesn't pause any deadline, but it sometimes resolves a dispute without a hearing.
For most California counties, the filing window for the regular assessment roll runs from July 2 through November 30. If you received a supplemental assessment notice - typically mailed after a recent purchase or new construction - the deadline is generally 60 days from the date on that notice, so check it carefully.