How Assessment Works: Market vs Assessed Value

A homeowner in Detroit pays an effective property tax rate of 3.02 percent on a median-valued home, while one in Honolulu pays a fraction of that — and neither number comes from the price the house would fetch on the open market. It comes from a figure a county assessor assigned, often years ago, using a methodology the owner never sees. That gap between what a property is worth and what it is taxed on is the single most misunderstood mechanic in residential real estate, and for households at the higher end of the market it routinely costs four and five figures a year.

Assessment is where the property tax bill is actually born. The rate gets the headlines, but the rate is applied to a number — the assessed value — that frequently bears little resemblance to the market value a buyer would pay today. Understanding how that number is set, how far it can legally drift from reality, and when the drift runs in the homeowner’s favor versus against it, is the difference between paying a fair bill and overpaying by default.

The Two Numbers That Decide Your Bill

Start with the distinction the entire system rests on. Market value is what a willing buyer would pay a willing seller today — the number a real estate agent quotes, the number Zillow estimates, the number that appears on a closing statement. Assessed value is the figure a county or municipal assessor assigns to your property for taxation. These are not the same thing, and in most jurisdictions they are not even calculated the same way.

Assessors arrive at assessed value through one of three approaches: the sales comparison approach (recent sales of similar properties), the cost approach (land value plus the cost to rebuild the structure, minus depreciation), or the income approach (used mainly for rental and commercial property). Residential assessment leans heavily on the first two. The catch is timing and ratio. Many jurisdictions assess at a fixed percentage of market value — the assessment ratio — and many reassess on multi-year cycles, which means the assessed value on your bill may reflect a market that no longer exists.

Consider how this plays out mechanically. A county assessing at a 50 percent ratio with a millage of 20 collects exactly half the tax of a county assessing at 100 percent with the same millage. A mill rate — the dollar amount of tax per $1,000 of assessed value — tells you nothing on its own, because the base it applies to is a moving, jurisdiction-specific target. This is precisely why comparing nominal rates across markets is close to meaningless, and why the effective tax rate — actual taxes paid as a percentage of market value — is the only figure that travels across state lines. A full breakdown of effective rates by county shows how wide that variation runs even within a single state.

Sources: Tax Foundation, Property Taxes by State and County, 2024 (CY2022 data); Lincoln Institute of Land Policy; IRS / One Big Beautiful Bill Act (Pub. L. 119-21, July 2025).

How Far Assessed Value Can Drift From Market Value

Reassessment cycles are where the gap opens. Some jurisdictions reassess annually; others run on three-, five-, or even longer cycles, and a handful effectively freeze assessed value until a property changes hands. In a flat market the drift is small. In a market that moved 30 percent in two years — which describes much of the country between 2020 and 2023 — a property assessed at the start of the cycle can carry an assessed value far below current market value, or, if values have since fallen, well above it.

That second case is the one homeowners miss. When assessed value exceeds market value, the owner is paying tax on wealth that does not exist. The correction mechanism is the property tax appeal (called a property tax protest in Texas and a handful of other states, where that is the statutory term). The math is direct: multiply the over-assessment by the effective tax rate, and you have the annual savings from a successful appeal.

Take a property carrying an assessed value of $1.2 million in a market where comparable sales support $1.0 million, in a county with a 1.8 percent effective rate. The $200,000 over-assessment translates to $3,600 a year in excess tax — recurring until corrected, and compounding across every year the error stands. Over a five-year reassessment cycle, that is $18,000 before any rate increases. The property tax appeal process is the only lever a homeowner controls directly; the rate is set by the taxing authority, but the assessed value is contestable.

States also limit how fast assessed value can climb. California’s Proposition 13 caps annual increases in assessed value at 2 percent until a property is sold, at which point it resets to market value — a structure that produces enormous disparities between long-held and recently purchased homes on the same street. The interaction of Prop 13 and luxury purchases is one of the clearest examples of assessment mechanics overriding market reality. Other states run their own caps, and the variation in property tax increase limits by state determines how much protection a homeowner actually has when values spike.

The Finluxy Property Tax Burden Index

Raw effective rates answer “what percentage,” but not “how does this market compare to the rest of the country.” The Finluxy Property Tax Burden Index normalizes every market against the national median effective property tax rate of 1.08 percent. The index is the local effective rate divided by 1.08 percent, expressed as a multiple: 1.0 sits at the national median, anything above 1.5 marks a high-tax market, and anything below 0.5 marks a low-tax one.

Index = state effective tax rate ÷ 1.08% national median. Effective tax rates: Tax Foundation, Property Taxes by State and County, 2024 (CY2022 data). National median per Lincoln Institute / Tax Foundation. Statewide medians; individual parcels vary.

The index reframes the spread. New Jersey at 1.93× is not “a bit higher than average” — a New Jersey homeowner pays nearly twice the national median rate on every dollar of market value, which is exactly why the New Jersey versus Texas comparison produces such different bills even on identically priced homes. Hawaii at 0.24× sits at roughly one-quarter of the median. On a $1 million market value, that difference is about $18,200 a year, every year, on the rate alone.

What Most Coverage Overlooks

Here is the finding that standard property tax coverage almost universally buries: the assessment gap and the federal SALT deduction cap now interact in a way that changes the entire calculus for high-value homeowners, and the 2025 law rewrote it. Most articles still cite the $10,000 SALT deduction (state and local tax) cap. That figure is obsolete. Under the One Big Beautiful Bill Act, signed July 2025, the cap rose to $40,000 for tax years 2025 through 2029, with a phase-out beginning at $500,000 of modified adjusted gross income, and a scheduled reversion to $10,000 in 2030.

Why this matters for assessment specifically: when the cap was $10,000, a homeowner in a high-tax state had already blown through the entire deduction with state income tax alone, meaning every additional dollar of property tax — including dollars from an inflated assessment — delivered zero federal benefit. The marginal value of an over-assessment correction was purely a state-level savings. At a $40,000 cap, more property tax now falls under the deductible ceiling for households below the $500,000 MAGI phase-out, which means an inflated assessment can cost a homeowner at the federal level too, by consuming deduction headroom that could have absorbed other state and local taxes. The appeal that was worth only its state-rate savings two years ago may now carry a federal dimension as well. The full SALT cap impact on deduction value turns on exactly where a household lands relative to that $500,000 threshold.

The second overlooked point is structural: high effective rates and high assessments are not the same problem and do not have the same fix. A high effective rate is a policy decision by the taxing jurisdiction — you cannot appeal it, only relocate away from it. An inflated assessment is an error or a lag — you can appeal it, and you should, because the rate then applies to a smaller, correct base. Conflating the two leads homeowners to either give up (“the rate is what it is”) or to appeal in markets where their assessment is already accurate and there is nothing to win.

The Assessed-Versus-Appraised Trap

One more distinction trips up even sophisticated buyers: assessed value is not appraised value. An appraisal is an independent professional estimate of market value, typically ordered by a lender at purchase or refinance. The assessed value is the assessor’s figure for tax purposes. A fresh appraisal can be powerful evidence in an appeal precisely because it documents market value independently — but the two numbers serve different masters and routinely diverge by wide margins. A bank appraisal coming in at $1.1 million does not automatically lower an assessed value of $1.3 million; it gives the homeowner the ammunition to argue the point, nothing more.

For properties at the upper end, the stakes scale with value. The mechanics of property tax on $2M-plus homes show how a single percentage point of over-assessment becomes a five-figure annual error. Special districts compound it further — Mello-Roos and special district taxes in California layer additional levies on top of the base assessment, and these often escape the effective-rate figures published at the state level entirely.

Methodology

What This Means for a $150k+ Household

For households at $150k+, three thresholds deserve attention. The first is the assessment-to-market gap on your own parcel: pull your current assessed value, compare it against recent comparable sales or a recent appraisal, and if the assessed figure runs meaningfully higher than defensible market value, the appeal math favors action — the over-assessment multiplied by your effective rate is a recurring annual cost, not a one-time hit. The second is the $500,000 MAGI phase-out on the expanded SALT cap. A household comfortably under it now has up to $40,000 of deduction room through 2029, which changes whether property tax is federally deductible at the margin; a household above it sees that room shrink back toward the $10,000 floor, restoring the old dynamic where high-state-tax residents get no federal value from incremental property tax. Knowing which side of $500,000 you sit on determines whether an assessment correction saves you at the federal level or only the state level.

The third is location itself. A Finluxy Property Tax Burden Index near 1.9× in New Jersey versus 0.24× in Hawaii is a structural cost that no appeal can touch — it follows the property, not the owner, and on a high-value home it dwarfs almost every other carrying cost decision. For a household weighing a relocation or a second property, the index is a cleaner signal than the sticker rate, because it strips out the assessment-ratio games and tells you, in one multiple, how a market taxes wealth relative to the rest of the country. The property tax guide for high-income homeowners works through how to fold that multiple into a total-cost-of-ownership model, where for most upper-bracket buyers property tax, not mortgage interest, is the line item that compounds least forgivingly over a long hold.