Adjusting comparables when nothing matches exactly
Small differences can be adjusted for. Large ones mean you picked the wrong comparable.
No two properties are identical. The question is not whether your comparables differ from your property but whether you have accounted for the differences honestly — and whether you needed to at all.
Uniformity often needs no adjustment
This is the first thing to understand, because it saves a great deal of work.
A uniformity comparison is already normalised by floor area — you are comparing assessed dollars per square foot. If your comparables genuinely match on class, neighbourhood, size band and age, the remaining differences are usually inside the noise, and adjusting for them invites argument about adjustments you cannot substantiate.
The better move is nearly always to tighten the group rather than adjust a loose one. Four properties needing no adjustment beat eight that need explaining.
When adjustment is genuinely required
Where no tight comparable exists. Unusual properties, very large lots, converted buildings, thin markets. Then you adjust, and you show your working.
How to do it defensibly
Adjust the comparable toward the subject, not the reverse. You are asking "what would this comparable be assessed at if it were like my property?"
Use the county's own rates where you can. If the assessor's schedule values a finished basement at a certain rate per square foot, use theirs. An adjustment drawn from the office's own figures is very hard to dispute.
Adjust for few things, not many. Each adjustment is an assumption. Three well-founded adjustments are credible; nine of them read as reverse-engineering a conclusion.
Show every step. Never present an adjusted figure without the unadjusted one beside it and the adjustment between them.
A worked example
| Comparable | Improvement | Area | $/sq ft | Adjustment | Adjusted |
|---|---|---|---|---|---|
| 1 — no garage; subject has none | $23,100 | 1,720 | $13.43 | none | $13.43 |
| 2 — has a finished basement | $27,400 | 1,780 | $15.39 | −$3,100 (county rate × 620 sq ft) | $13.65 |
| 3 — no garage | $22,600 | 1,690 | $13.37 | none | $13.37 |
What not to adjust for
- Décor and taste. Not assessed.
- Who the neighbours are. Not assessed.
- Ordinary wear. Already in the depreciation the model applies.
- Anything you cannot put a sourced number on. An adjustment you cannot justify is worse than none, because it makes the whole table look constructed.
The honesty test
Adjust in both directions. If every adjustment you have made happens to move the figure your way, an analyst will notice, and reasonably conclude the adjustments were chosen for their effect. A table containing one adjustment against your own interest is dramatically more persuasive than one that does not.