Assessed Value

Market value is what a buyer would pay; assessed value is what the tax collector uses, and the two diverge by design in many states. Some assess at full market value, others at a statutory fraction (an assessment ratio), and some cap how fast the assessment can rise regardless of prices, most famously California’s Proposition 13, which limits growth to 2 percent a year until the property sells. Published effective tax rates bridge these differences by expressing the actual tax as a percent of market value.

Assessments are also the appealable half of the tax bill. You cannot argue with the rate, but every county runs an appeal window where comparables showing your assessment above market reality can lower it, and such appeals succeed routinely. The property tax calculator works in effective-rate terms so the state-by-state assessment quirks stay out of your math.