Every homeowner gets the bill, but the bill's arithmetic is rarely printed on it: a total, a due date, and a value that may or may not resemble what the home would sell for. The calculation itself is short — value, minus exemptions, times rate — and each of its three numbers has its own owner: the assessor sets the value, the law sets the exemptions, and the local budgets set the rate. This page is the three steps, the three different values that get confused for one another, and the reasons a bill moves in a year when nobody raised a rate.
Property tax starts with an estimate, not a sale: the county or municipal assessor values every property in the jurisdiction, usually by mass appraisal — recent sales of similar homes, adjusted for size, age, condition and lot, applied across whole neighborhoods at once rather than home by home. That produces an estimate of market value as of the jurisdiction's valuation date, which is why the number can lag a fast market in either direction: it describes the home on the assessor's date, under the assessor's schedule, and reassessment happens on the jurisdiction's cycle — yearly in some places, every few years in others — not when the market moves.
The estimate is then converted by the assessment ratio, the percentage of market value the jurisdiction actually taxes. At 100% the assessed value is the market estimate itself; at a lower ratio it is a fixed fraction of it. The ratio is set by state or local law, applies uniformly to properties in the same class, and — on its own — neither raises nor lowers taxes: a jurisdiction taxing 25% of value simply sets its rate against that smaller base. What the ratio does explain is the notice that looks impossible: an assessed value a quarter of the home's sale price is not a gift or an error, it is the arithmetic working as designed.
From the assessed value come the subtractions. Exemptions — the homestead exemption for a primary residence is the near-universal one; senior, veteran and disability exemptions layer on in many places — remove a set amount or percentage before any rate is applied. Some jurisdictions also cap how fast a homesteaded home's taxable value may rise each year, which is why long-held homes often carry taxable values well below both of the numbers above them in the chain. What survives the subtractions is the taxable value, and it — not the Zestimate-style market number, and not the assessed value — is the figure your bill is actually figured on.
The last step is the rate, and it belongs to the budgets, not to your house. Each taxing district over your home — county, city, school district, and special districts for fire, water, libraries or transit where they exist — works out what it must raise from property tax and divides that across the total taxable value inside its borders. The result is that district's levy, usually stated in mills: one mill is $1 per $1,000 of taxable value. Your bill applies the sum of every levy whose district contains your home, which is why two identical houses in different school districts — or on opposite sides of a city line — can owe different taxes on the same value.
Homeowner HQ keeps the homeowner's side of the record straight between sales: your own agent's monthly updates track your home's value and equity, and the fix-my-facts route keeps the facts behind them corrected. The tax chain is a fact with the same need: the value your agent reports is a market estimate, the assessor's numbers are a different chain built for a different purpose, and knowing which number a notice is using — market, assessed, or taxable — is the difference between spotting a real error worth appealing and arguing with arithmetic that was never wrong.
In three steps, and only the last one is a rate. First, the local assessor estimates the home's market value and converts it into an assessed value: some jurisdictions assess at the full market value, others at a set percentage of it, called the assessment ratio. Second, any exemptions the owner qualifies for — the homestead exemption is the common one — are subtracted from the assessed value, leaving the taxable value. Third, the local tax rate is applied to the taxable value. The rate is usually stated in mills: one mill is $1 of tax for every $1,000 of taxable value, so 20 mills is a 2% rate. One labeled illustrative example only: a home with a $300,000 taxable value at 20 mills owes $300,000 ÷ 1,000 × 20 = $6,000 for the year. The rate itself is not one government's number — it is a stack of levies from every taxing district the home sits in (county, city, school district and any special districts), each set from that district's budget divided across the taxable value of all the property in it.
They are three different numbers for the same house, in a chain. Market value is what the home would likely sell for — the assessor's starting estimate, built from recent sales of similar homes. Assessed value is the share of that market value the jurisdiction chooses to tax: at a 100% assessment ratio it equals the market value; at a 25% ratio a $400,000 home carries a $100,000 assessed value. Taxable value is what is left of the assessed value after exemptions are subtracted — the number the rate is actually applied to. Confusing the three is the most common reason a tax notice looks wrong when it is not: a home can gain market value while its taxable value barely moves, because an assessment cap or an exemption absorbed the change, and it can show an assessed value far below its sale price without any error at all, because the ratio did that on purpose.
Because the rate is only one of the two moving parts — the taxable value underneath it moves too. A reassessment that lifts your home's assessed value raises the bill at the same rate. Losing an exemption does the same thing in one step: a homestead exemption that ends because a home was sold, rented out or stopped being a primary residence puts the exempted value back into the taxable column. New or higher levies inside the stack can also raise the combined rate while the headline rate a homeowner remembers stays put. And where the bill is paid through a mortgage escrow account, the servicer's annual escrow analysis spreads any increase — plus any shortage from the year just ended — across the next year's payments, so the monthly change can be larger than the tax change itself. The notice shows which part moved: compare this year's assessed and taxable values against last year's before comparing rates.
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