How do I adjust comps for square footage differences?
How do I adjust comps for square footage differences?
Estimate a local price-per-square-foot for the difference, then add to or subtract from the comp's sale price: if a comp is larger than your home, lower its price; if smaller, raise it — so each comp reflects what it would have sold for at your home's size.
Adjusting comps for size is the single most common adjustment in a residential appeal, because few comparable sales match your home's square footage exactly. The goal of any adjustment is to restate each comp's sale price as what it would have sold for if it were like your home. This mirrors the sales comparison approach the IAAO Standard on Mass Appraisal of Real Property identifies as preferred for residential property.
Step 1 — Get the right square footage for both. Use the livable / heated area assessors use, not gross or lot area. Confirm your own square footage from your property record card; a record error here is itself a strong appeal (see the wrong-square-footage question).
Step 2 — Estimate a per-square-foot adjustment rate. This is NOT the home's full price per square foot. A house's land, location, and base structure don't scale linearly with size, so the marginal value of an extra square foot is smaller than the average. A common approach: derive it from paired sales (two similar homes that differ mainly in size) or use a conservative figure well below the overall $/sf. Show how you got the number.
Step 3 — Apply the adjustment in the right direction:
- Comp is LARGER than your home → subtract value (the comp "should" sell for less at your smaller size).
- Comp is SMALLER than your home → add value.
Example: a comp sold for $400,000 and is 200 sq ft larger than your home. At a marginal rate of $50/sf, subtract 200 × $50 = $10,000, giving an adjusted indicator of $390,000 for your home.
Step 4 — Build an adjustment grid. List each comp, its sale price, the size difference, the adjustment, and the adjusted value. The board can follow your logic at a glance, and the Texas Comptroller lists comparable-property information among the evidence to present — a transparent grid is far more persuasive than raw sale prices.
Practical tips: adjust for other big differences too (lot size, pool, garage, age, condition), keep total adjustments modest, and prefer comps that need the least adjustment. A comp requiring a 40% size adjustment isn't really comparable.
State-by-State Variations
| State | Exception or Variation |
|---|---|
| Texas | Texas — for an equal-and-uniform protest, [Tex. Tax Code §41.43(b)(3)](https://statutes.capitol.texas.gov/Docs/TX/htm/TX.41.htm) requires comparable properties be "appropriately adjusted," so a documented size adjustment is part of the statutory standard, not optional polish. |