What Evidence Actually Wins a California Property Tax Appeal?
Recent sales of homes that look like yours, sold close to January 1, with adjustments. Property Tax Rule 4 spells it out — and it's narrower than most homeowners expect.
The short answer: recent sales of homes that look like yours, sold close to January 1 of the year you're appealing, with adjustments for the differences. Everything else — Zillow estimates, your neighbor's tax bill, a hot take about the market — does not move an assessor or an appeals board. California Property Tax Rule 4 spells out what's required, and it's narrower than most homeowners expect.
This page walks through what counts, what doesn't, how many comps you actually need, and what to do if your property is too unusual to have good comps.
What evidence do I need for a property tax appeal in California?
You need three things, in this order: (1) your property's assessed value (from your tax bill or assessment notice), (2) recent comparable sales — typically three to five — that closed close to the January 1 lien date, and (3) adjustments that explain how those comps differ from yours.
If you're appealing a decline in value (Prop 8 / R&T § 51(a)(2)), the lien date you're proving market value as of is January 1 of the current roll year. If you're appealing a change-in-ownership assessment, the valuation date is your closing date. If you're appealing new construction, it's the date construction was complete. The valuation date is the moment in time you're trying to prove a value for.
What counts as a “comparable sale”?
A comparable sale is a recent, arms-length sale of a property similar to yours in size, condition, age, location, and use. California Code of Regulations Title 18 § 4 — Property Tax Rule 4 — is the controlling rule, and Revenue & Taxation Code § 402.5 sets the legal floor for what an appeals board can consider.
The 90-day rule
This is the rule that surprises most homeowners. Under R&T § 402.5, an assessment appeals board cannot consider any sale that closed more than 90 days after the valuation date. For a regular (Prop 8) appeal with a January 1 lien date, that means no sale closing after roughly March 31 will be considered. There's no limit on how far backward in time a comp can be — the law only restricts how far forward. An assessor following the BOE's Assessors' Handbook Section 502 applies the same rule.
That's why an appeal you start in October needs to be built around sales that closed before March 31 — even though “more recent” sales feel intuitively stronger.
Similarity (size, age, condition, location)
R&T § 402.5 requires comparable sales to be “sufficiently alike in respect to character, size, situation, usability, zoning or other legal restrictions” to make the comparison meaningful. In practice, a 1,400-square-foot 1960 ranch with three beds and two baths is most credibly compared to other 1,200–1,600-square-foot mid-century three-bedroom homes — not to a 2,500-square-foot remodel, even if it's on the same street.
How close geographically?
There's no statutory distance, but Property Tax Rule 4(d) requires the assessor (and appeals board) to make adjustments for “location of the properties.” The closer the better — same neighborhood, same school district, same side of the freeway. Cross-town comps almost always require larger location adjustments that weaken your case.
How do adjustments to comps work?
Adjustments translate “this comp sold for $X” into “this comp, if it were like my home, would have sold for $Y.” Property Tax Rule 4(d) requires assessors to make adjustments for differences in “physical attributes of the properties, location of the properties, legally enforceable restrictions on the properties' use, and the income and amenities which the properties are expected to produce.”
Square footage and bed/bath
The most common adjustment. If your home is 1,400 sq ft and a comp is 1,600 sq ft, you subtract value from the comp — typically a per-square-foot dollar figure derived from local market data. Same logic for an extra bath or bedroom.
Condition and deferred maintenance
If your home has a 25-year-old roof, original kitchen, and a sloping foundation, and the comp was renovated last year, you subtract from the comp's price. Photos, contractor estimates, and inspection reports dated to the lien date are how you prove condition.
Time adjustments
Property Tax Rule 4(c) requires conversion of a sale to the valuation date by adjusting for any change in the price level “of this type of property” between when the sale closed and your lien date. If your comp closed in October but your lien date is January 1, you adjust for any price movement in those three months. In a falling market, that means adjusting the October price downward.
Lot size and view
Same principle: bigger lot, view of the bay, corner location, busy street — all are adjustment items if they materially affect price.
This is what Overassessed does
We find comparable sales from county records, calculate professional-grade adjustments for differences in size, features, and condition, and package the evidence — ready to submit.
How many comparable sales do I need?
There's no statutory minimum. BOE Publication 30 (Residential Property Assessment Appeals) doesn't set a number — but appeals boards routinely look for a minimum of three closed sales, with five being more persuasive. The LA County Assessor's RP-87 informal-review form recommends 3-to-5 comps that closed no later than March 31 of the appeal year.
What if my property is unique and there are no good comps?
Property Tax Rule 3 lists three permitted approaches to value: the comparative sales approach, the cost approach (Property Tax Rule 6), and the income approach (Property Tax Rule 8). If sales comps are scarce or unreliable, the assessor and the appeals board can consider the others.
The cost approach
Cost is “the cost of replacing reproducible property with new property of similar utility, less depreciation.” It's most useful for new construction, very recent renovations, or single-purpose buildings. For a typical resale single-family home, comp sales almost always beat cost.
The income approach (briefly, for non-SFR properties)
For multi-family, commercial, or any property typically purchased for cash flow, the income approach capitalizes the property's net income stream into a present value. It's outside the scope of what most homeowners need and outside Overassessed's MVP. If you own a small apartment building or commercial property and want to appeal, plan to bring rent rolls, expense statements, and a market-derived capitalization rate. One important note: the 90-day rule does NOT apply to sales used to derive a cap rate under the income approach — a 1996 BOE Annotation and the Bank of America v. County of Fresno case both confirm that. That gives income-approach appeals more flexibility on data.
What evidence does NOT work?
Things California homeowners often try that don't move the needle:
- Zillow Zestimate, Redfin Estimate, or any automated valuation model. No California assessor or appeals board treats AVMs as competent evidence. They're not based on the lien date, they're not adjusted, and they're not transparent about methodology.
- Your neighbor's lower tax bill. Different base years under Prop 13 produce wildly different tax bills for similar homes. The Orange County Assessor specifically warns that “the value of your property usually has nothing to do with the value of your neighbor's property.”
- Listings (asking prices). Listings are offers, not sales. Property Tax Rule 4 deals only in sale prices.
- A general “the market is down” argument. California assessment is property-specific. You have to prove a value for your property as of your lien date.
- Sales that closed more than 90 days after the lien date. Excluded by R&T § 402.5.
- Foreclosure or auction sales. BOE Annotation 848.0003 holds that foreclosure auctions are “forced sales” not considered open-market transactions, and the purchase-price presumption does not apply. They can sometimes be considered if you can show the foreclosure depressed the whole neighborhood, but you'd lead with arms-length sales first.
Can I see the assessor's evidence before the hearing?
Yes. Under R&T § 1606 and Property Tax Rule 305.1, you can request a written Exchange of Information with the assessor. If your property's assessed value (before exemptions) is $100,000 or less, only the applicant can request the exchange. If the value is above $100,000, either party can request it — and almost all California single-family homes will be above that floor, so this is the norm for homeowners.
The request has to be filed at least 20 days before the hearing. Each side then exchanges valuation evidence and the basis for their opinion of value. After the exchange, neither side can introduce new evidence at the hearing without the other party's consent. This is the cleanest way to see the assessor's case before you sit down.
Informal review vs. formal appeal: where does evidence get submitted?
This varies by county — see the individual county pages on Overassessed for specifics. The general framework:
- Informal review evidence goes to the assessor's office on the county's decline-in-value form. The form is usually short, and you submit it with copies of comparable sales and any other supporting documents. There's no hearing. The assessor either agrees and lowers your value or doesn't.
- Formal appeal evidence goes to the Clerk of the Board of your county on form BOE-305-AH — Assessment Appeal Application. After filing, you'll have a hearing where you present evidence to the Assessment Appeals Board (or a hearing officer in eligible cases).
The two paths are independent. Most counties — including Alameda, San Mateo, Santa Clara, San Diego, and Orange — explicitly recommend filing the formal appeal even if your informal review is still pending, so you don't lose appeal rights if the informal answer comes back after the formal deadline.
For the specific deadlines in each county, see California property tax deadlines by county.
Who has the burden of proof?
In most appeals, the applicant has the burden of proving the assessor's value is wrong — under Property Tax Rule 321, the assessor's value is presumed correct. But for an owner-occupied single-family residence, the burden shifts to the assessor to affirmatively prove their value by a preponderance of the evidence — if the homeowner has supplied the assessor with all the information required by law. That's a meaningful homeowner advantage that most appeal services don't bother to mention.
Frequently asked questions
For a regular Prop 8 appeal, sales need to have closed no more than 90 days after January 1 of the appeal year — under R&T § 402.5. There's no limit going backward in time, but in practice sales closer to the lien date are stronger. For a change-in-ownership appeal, the 90-day window runs from the closing date, not January 1.
A licensed appraisal effective as of the lien date is acceptable evidence. The appraiser still has to use comps that meet the 90-day rule and Rule 4 adjustments, but a credible written appraisal is one of the strongest forms of evidence a homeowner can bring. It's not required.
That's a factual error — usually fixed faster through an informal review than a formal appeal. Show the county tax-roll record, your real square footage (a recent appraisal, MLS listing from when you bought, or county building department record), and ask for a correction. Counties typically fix obvious data errors quickly; valuation disputes go through the longer review process.
Yes. The instructions on the BOE-305-AH appeal application say plainly: filing an application for reduced assessment does not relieve the applicant from the obligation to pay the taxes on the subject property on or before the applicable due date shown on the tax bill. If you win, you get a refund with statutory interest.
Yes — that's why you should think hard before filing if your case is weak. R&T § 1610.8 and the BOE-305-AH instructions both confirm that based on the evidence submitted at the hearing, the appeals board can increase, decrease, or not change an assessment. In practice, increases are rare on residential decline-in-value appeals — but legally possible.
Two years from the date a complete application is timely filed, under R&T § 1604. If they don't decide within two years, the applicant's opinion of value generally becomes the value — though there are conditions, and counties can request waivers.
A short evidence checklist
- Three to five recent sales that closed before/around your lien date and no later than 90 days after
- Each comp similar in size, age, condition, bed/bath, and location to your property
- Adjustments documented in writing — square footage, condition, time, lot, view
- Photos of any condition issues (deferred maintenance, damage, view obstructions) dated to the lien date
- Your county's informal review form OR BOE-305-AH for the formal appeal
- A written opinion of value (your bottom line, in dollars)
- Optional: an Exchange of Information request under R&T § 1606 to see the assessor's case before the hearing
Our Filing Guide pulls comps that meet the 90-day rule, applies the adjustments, and packages everything for submission.
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Overassessed provides estimates based on publicly available data and AI-generated analysis. This is not a formal appraisal, legal advice, or tax advice. Results are not guaranteed, and appeal outcomes depend on county review. Users file their own appeals. AI-generated estimates may differ from actual market values.