Mass appraisal is the method appraisal districts use to value thousands of properties simultaneously rather than appraising each one individually. It relies on statistical modeling, comparable sales analysis, and property characteristics to estimate values at scale.
Unlike a private appraisal where an appraiser visits your home and makes individual judgments, mass appraisal uses computer models that apply valuation factors to groups of similar properties. An appraiser might never set foot on your property.
Mass appraisal is necessary—counties can't individually appraise millions of properties annually—but it's imperfect. The models make assumptions that don't always fit your specific situation.
Understanding mass appraisal reveals why protests often succeed. The system has built-in limitations:
What mass appraisal misses:
• Interior condition (they can't see inside)
• Deferred maintenance
• Outdated kitchens/bathrooms
• Functional problems
• Unique negative features
Common errors:
• Wrong square footage in records
• Features you don't have
• Condition rated too high
• Poor comparable selections
Your protest is the opportunity to provide information the mass appraisal system missed. Photos, condition evidence, and better comparables can overcome the model's assumptions.
How mass appraisal works:
Data collection:
• Property characteristics from records
• Sales data from recent transactions
• Building permits and improvements
• Aerial imagery and public records
Model building:
• Group similar properties
• Analyze how features affect sale prices
• Create valuation formulas
• Apply models to all properties
Result:
Your assessed value is calculated by a formula, not by someone evaluating YOUR specific home.
Example formula: Base value + ($/sq ft × square footage) + pool adjustment + location factor = assessed value
Probably not, unless you requested an interior inspection or your home was recently built. Mass appraisal relies on external observations, permit records, and statistical models. The county assumes average condition unless you prove otherwise.
Mass appraisal models consider property characteristics: square footage, lot size, year built, improvements, etc. Even similar-looking homes can have different values based on recorded features. Check your property record card for errors that might explain differences.
The county won't provide individual appraisals, but you can request an interior inspection if you believe your condition is worse than assumed. During protests, you can also submit your own private appraisal as evidence.