Homeowners encounter multiple different statements about their home’s “value” — the Zillow estimate that updates weekly, the appraised value from their mortgage application, the assessed value on their property tax bill — and these numbers often differ from each other, sometimes dramatically. Understanding that each measurement serves a distinct purpose and is calculated using different methodologies explains why they diverge and helps you evaluate each appropriately for its relevant purpose. It also equips you to challenge valuations that affect real financial outcomes — property taxes and mortgage terms — when they appear to be wrong.
Market Value: What a Buyer Would Actually Pay
Market value is the price at which your home would sell in a competitive market between an informed, willing buyer and an informed, willing seller, neither under undue pressure to transact. It is the conceptual benchmark against which other valuation methods are measured, but it is not directly observable until an actual transaction occurs. Automated valuation models — Zillow’s Zestimate, Redfin’s estimate, and similar tools — attempt to approximate market value using algorithms that incorporate recent comparable sales, property characteristics, and neighborhood trends. These estimates provide useful directional information but can be significantly inaccurate for specific properties, particularly unusual homes, homes in areas with few recent sales, and homes that have been significantly renovated or deteriorated from typical neighborhood condition.
A comparative market analysis prepared by a real estate agent — comparing your home to recent sales of similar properties in your neighborhood — provides a more reliable market value estimate than automated models because it incorporates professional judgment about the comparability of specific sales. An actual appraisal provides the most defensible market value estimate, using a rigorous methodology that is the basis for lending decisions.
Appraised Value: The Lender’s Collateral Assessment
When you borrow money secured by real estate — a mortgage, refinance, or home equity loan — the lender hires an independent appraiser to assess the property’s value as collateral for the loan. The appraisal determines the maximum loan the lender will extend relative to the property’s value (the loan-to-value ratio) and protects the lender against lending more than the collateral is worth. Appraisals use a formal methodology: selection and adjustment of comparable sales, consideration of the income approach for investment properties, and assessment of cost factors for new or unique properties. The resulting appraised value is a professional opinion of market value based on the available evidence at the time of the appraisal.
When an appraisal comes in below the agreed purchase price — a “low appraisal” — it creates a negotiating problem: the lender will not lend against the higher price, requiring either a price reduction, a larger down payment from the buyer, or cancellation of the transaction. If you believe a low appraisal is inaccurate, you can provide the appraiser with comparable sales they may have overlooked — specifically sales of similar properties at higher prices — and request reconsideration. Appraisers are required to consider relevant comparables submitted by interested parties, though they are not required to change their opinion. A second appraisal is another option when the first seems clearly deficient.
Assessed Value: The Tax Authority’s Calculation
Assessed value is determined by your local government assessor and used to calculate your property tax bill. Property taxes are calculated by multiplying the assessed value by the local tax rate (the mill rate). Most jurisdictions assess property at some percentage of market value — in some states at full market value, in others at 50 or 70 percent of market value — and the applicable percentage is called the assessment ratio or equalization rate. If your county assesses at 80 percent of market value and your home has a market value of $400,000, your assessed value would be $320,000, and your property taxes would be calculated on that $320,000 base.
Property tax assessments can be incorrect, and challenging an incorrect assessment is your legal right and often financially worthwhile. Most jurisdictions have a formal appeals process with specific deadlines — missing the appeal deadline forfeits the right to challenge that assessment year. Successful challenges typically require evidence that the assessed value exceeds market value — comparable sales at lower prices, a current appraisal below the assessed value, or documentation of property defects not reflected in the assessment. Local property tax appeals attorneys or consultants work on contingency — they receive a percentage of the tax savings from a successful appeal — which makes challenging an incorrect assessment financially accessible even for homeowners who cannot fund the challenge upfront.