Every year the local tax office assigns a value to each property for the purpose of collecting property taxes. That official valuation is the assessment. It may differ from market value and is governed by state and local rules.

Assessors use mass-appraisal techniques, reviewing sales data, property characteristics, and sometimes interior inspections. Homeowners receive an assessment notice and usually have a window to appeal if they believe the figure is too high. Successful appeals can lower the tax bill for years.

Assessment ratios and equalization rates vary by jurisdiction. Some areas assess at full market value; others use a fraction. Special assessments may also appear for local improvements such as sidewalks or sewers. Understanding the assessment process helps owners anticipate tax costs and challenge errors.

• Official valuation used for property taxation
• May differ from current market value
• Subject to owner appeal in most places
• Determines the size of the annual tax bill