Methodology

California taxes a home on its Proposition 13 base: the price paid when it last changed hands, grown by no more than 2% a year. Proposition 8 lets the Assessor set a lower value for a single year when the home's market value on January 1 has fallen below that base. So the question is not whether a home is assessed above its neighbors, as it is in Georgia, but whether it is worth less today than the owner paid for it.

That makes recent buyers the whole subject. We analyze single-family homes and condominiums whose Proposition 13 base year is 2022 or later, in the three counties where we operate. A home bought earlier is almost always assessed well below its market value already, and we say so rather than score it (§2).

Every figure is as of the lien date, January 1, 2026, for the 2026–27 roll. The County value we compare against is the value the County carries for the home on that roll. Where the County has not yet published it, we use the prior roll's value, or, for a home bought during 2025, the recorded purchase price (plus the 2% inflation factor for a purchase in the first half of the year, which is how the Revenue and Taxation Code enrolls it). A 2026 value the owner enters from their own bill replaces that figure; it is the County's own number and is checked against the Assessor's parcel page.

These exclusions happen before any home is scored. They shape the universe and the pool of sales the readings are allowed to learn from.

Long-held homes

A home whose base year is before 2022 is not scored. Proposition 13 has kept its assessed value below market for years, so a decline-in-value request would ask the Assessor for a value above the one it already carries. The site tells these owners that plainly instead of showing an estimate.

Purchases after the lien date

A home bought on or after January 1, 2026 is not on the 2026–27 roll at its new price; the roll still carries the seller's value, and the purchase price arrives through a supplemental assessment. A review of the roll value would save the buyer nothing this year, so the home is not scored.

Transfers that are not sales

A parent-to-child transfer, a trust reshuffle or a partial interest records a deed but does not reset the Proposition 13 base. The sales readings use only recorded market sales, and a home enters the pool only when its base year matches the year its deed was recorded.

Declared-disaster areas

In ZIP codes touched by the 2025 Eaton and Palisades fires, sales of cleared lots pull a neighborhood median far below what a standing house is worth. No home in those ZIPs is scored; the site points those owners to the Assessor's own misfortune-and-calamity relief instead.

County values that cannot be right

Where the County value sits 50% or more above both readings, the problem is the County figure, not the market: a multi-parcel deed recorded against one parcel, a price back-derived from a city transfer tax, or an estate lot neither reading can see. These homes are held out, not flagged.

Every California figure rests on two independent readings of the home's market value on the lien date.

The comparable-sales reading

The median price per square foot of recorded market sales of homes of the same type and similar size in the home's valuation group (Figure 1), multiplied by the home's own living area. Prices are the recorded purchase amounts. This is the reading a homeowner can check with their own eyes against the sales printed in their Package.

The automated valuation

A commercial automated valuation model built from the County's own recorded sales, obtained for each home individually. It anchors on the home's own last sale and its recorded characteristics, so it sees things a neighborhood median cannot, and misses others.

The opinion of value

Our opinion of value is the higher of the two readings. Since September 24, 2026 it is also never set below what the sales printed in the Package imply at their lowest price per square foot; where that floor sets the figure, the Package says so. (Homes whose letter was mailed before that date keep the figure their letter printed.) Where no automated valuation exists for a home, there is one reading and no figure is shown (§6).

The gap and the saving

The gap is the County value less the opinion, as a share of the County value. A home is a case when the gap is 5% or more. The estimated saving is the difference multiplied by the home's own tax rate from the County's records (1.2% where we have none), for one year: a Proposition 8 reduction is re-determined every year (§7). For our mailing lists we apply a second floor of $1,000 a year in estimated saving, so that a letter is only sent where the saving is worth the owner's time.

A fair question is why an advocate for the homeowner would choose the reading that asks for less. Three reasons, and we state them because the owner attests to this figure under their own signature.

A neighborhood median is a screen, not an appraisal. Tested against sales it had not seen, the comparable-sales reading on its own misses a typical home's price by more than the 5% gap we look for. Worse, when you sort homes by how far the County value sits above such a reading, the biggest apparent gaps are disproportionately the homes the reading undervalued: the well-finished house on an ordinary block. Using it alone would select our own errors.

The two readings miss different things. Both come from public records, and neither sees a home's condition or finish. The automated valuation anchors on the home's own last sale, so it is a second opinion rather than a referee. Where they disagree, the honest reading of the evidence is the reduction both support, which is the higher of the two.

The figure has to survive the Assessor's review. An appraiser reads the owner's opinion beside the sales the owner lists and any others on file. An opinion that one method supports and another contradicts invites the Assessor to substitute its own number, and the Assessment Appeals Board can raise a value as well as lower it. A figure both readings support is the one we are willing to put our name behind.

It remains the owner's opinion. The Package shows the lower reading wherever the owner's own listed sales do not contradict it, and the owner may enter that figure, or any figure they can support, instead of ours. We will learn from the Assessor's decisions which reading came closer, and this page will record any change to the rule.

The sales printed in a Package, and listed on the County's form, are examples chosen from the recorded sales the reading was built on. Each is a recorded market sale of a home of the same type and similar size, nearest to the subject (within a mile wherever two such sales exist), closest in time to January 1, 2026, and sold for less than the County's value. Sales are used through March 31, 2026: the Revenue and Taxation Code lets the Assessor consider a sale after the lien date only within 90 days of it.

The sales are context for the Assessor, not the arithmetic behind the opinion, which is set as §3 describes; the Package says which. Each county's form accepts a request without comparable sales, and the Assessor reviews the value on its own either way.

Two checks run before a home is priced. Where the sales the Package would print imply a value at or above the County's, the Package's own evidence would argue against the owner, and the home is not priced. And where most nearby sales of similar size sold above the County value, a sign there may be no case at all, the home is moved to a closer look and shows no figure.

A home shows a dollar figure only when both readings exist and agree on a case. Everything else falls into one of three answers, and they are different answers.

“Worth a closer look”

The comparable-sales reading sits below the County value, but there is no automated valuation for the home yet, or the estimated saving is $15,000 a year or more, or the nearby sales point the other way (§5). One reading is not enough to put a number in front of a homeowner, so we show none. A County value the owner enters from their bill does not change this: the missing piece is the second reading, not the denominator.

“We don't see a case”

Both readings exist and the County value is at or below the opinion, or within 5% of it. This is a conclusion, not a set-aside: the evidence we have says the home is not over-valued. It can be wrong in the direction opposite to our lists, for the below-average house on a good block, which is why the site points these owners to the Assessor's public parcel page and to the County's free review.

Held out

The exclusions in §2: long-held homes, purchases after the lien date, disaster ZIPs, and County values that cannot be right. The site says which applies. No County value the owner supplies rescues a held-out home, because the problem is the reading, not the comparison.

Unlike the Georgia engine, the California models carry no numeric confidence score. The second reading does that work: a home is priced when the readings agree, and not priced when they cannot be compared.

Five things this work deliberately does not claim to be.