What Is Size Adjustment
A size adjustment is a mathematical correction applied to a comparable property's sale price to account for differences in building square footage or lot size between that comparable and your subject property. Appraisers use this adjustment when finding truly comparable sales is impossible, which happens often in specialized markets or unique locations.
During a property tax assessment appeal, the assessor's office and your appraiser will both use comparable sales to estimate your property's market value. When those comps differ meaningfully in size, the adjustment bridges the gap. For example, if a comp sold for $400,000 with 3,000 square feet, but your property is 3,500 square feet, an appraiser might adjust the comp's price upward to reflect what that larger property would likely fetch in the same market.
How Size Adjustment Works in Appeals
Assessors typically apply size adjustments using one of two methods. The market extraction method analyzes multiple sales of similar properties at different sizes to determine a per-square-foot adjustment rate specific to your market and property type. The second approach uses a standard percentage adjustment, though this is less defensible in a board of review hearing.
The calculation is straightforward: if your comp sold at $150 per square foot and your property is 500 square feet larger, you'd adjust that comp's value upward by $75,000 (500 sq ft × $150). However, the challenge lies in determining the correct per-square-foot rate for your specific property type and location. This rate varies dramatically. A 1,000-square-foot addition to a suburban ranch home might command $125 per square foot, while the same addition to an urban townhouse could be worth $300 per square foot or more.
Assessment ratios in your state also affect how size adjustments impact your final appraised value. If your state uses a 50% assessment ratio, the appraised value is reduced by half before calculating your tax bill. This means size adjustments matter less in terms of absolute dollars owed, but they still influence whether your assessment meets legal standards for uniformity.
Size Adjustment at Board of Review Hearings
When you appeal your assessment, expect the assessor to defend size adjustments using recent comparable sales data. Bring your own adjusted comps to challenge their methodology. The board will scrutinize whether the per-square-foot adjustment rate is defensible within your local market. If the assessor used a flat 8% adjustment while market data supports only 3%, you have strong grounds to challenge the adjusted value.
Documentation matters here. Pull sales of properties similar to yours that differ by 500, 1,000, or 1,500 square feet. Show the price differences and calculate the implied per-square-foot adjustment that the market actually supports. If local MLS data shows properties in your neighborhood at $140 per square foot for comparable features, use that figure consistently.
Common Pitfalls
- Using national or regional per-square-foot averages instead of neighborhood-specific data. Your 2,500-square-foot home in a neighborhood where comps average 2,000 square feet will not command the same per-square-foot rate as comps in a neighborhood where homes average 3,500 square feet.
- Ignoring quality and condition differences. A size-adjusted comp in poor condition will overstate the value of your well-maintained property. Adjustments should account for condition separately from size.
- Relying on tax-assessed values of comps rather than actual sale prices. The assessor's office may have adjusted those comps inappropriately, which corrupts your adjustment calculation.
- Failing to adjust for time. A comp from 18 months ago needs a time adjustment in addition to size adjustment, and these compounds.
Common Questions
What if my property and the comp are both large outliers in the neighborhood?
Size adjustments become unreliable when you're adjusting between two properties that are both significantly larger or smaller than typical homes in the area. In this case, push back at the board of review and ask why the assessor didn't locate more comparable properties. If 80% of homes in your neighborhood are 2,000 to 2,400 square feet, comparing a 3,200-square-foot home to comps and adjusting them heavily for size is not defensible. The assessor should search a broader geographic area for properties more similar to yours in size.
How much per square foot should I use for my size adjustment?
Use market data specific to your property type and neighborhood, not generalized figures. Pull MLS sales data for the past 12 months of properties similar to yours. Calculate the price per square foot for each. The median or mean of that group is your justified adjustment rate. If you're in a state with a state appraiser board, check if they've published recommended rates for your county and property type, though these should be validated against local data.
Can I use size adjustments to argue my assessment is too high?
Yes, but only if the assessor's size adjustment was too aggressive. For instance, if the assessor adjusted a 2,000-square-foot comp to 2,500 square feet (your property) using $200 per square foot, but neighborhood data supports only $120 per square foot, the overadjustment inflated your assessed value. Demonstrate the correct rate to the board and request a downward adjustment.