How Comparable Homes Are Chosen, and Why It Matters

What assessment offices ask for

Each office sets its own expectations, and they are specific:

• Cook County Assessor: if you use comparable properties, at least 3 are required and 5 are recommended. They should be in your assessment neighborhood and similar to your home.
• Cook County Board of Review: compare your home with properties in the same neighborhood and the same classification code. Uniformity is compared as building assessment divided by building square feet, and sales of similar homes within the last 3 years can be used as evidence.
• Illinois boards of review generally hear appeals showing that similar neighboring homes are assessed lower.
• California appeals boards consider comparable sales, replacement cost or income; for homes, sales of similar properties are usually the most reliable. A board can't admit comparable sales dated more than 90 days after the valuation date, which is January 1 of the year you file.
• Texas appraisal review boards decide an unequal-appraisal protest for the owner unless the appraisal district shows the home's appraised value is at or below the median appraised value of a reasonable number of comparable properties, appropriately adjusted.

Two kinds of comparison

Uniformity compares assessments with assessments: is your home assessed higher than similar homes? It doesn't need recent sales, only consistent records. Cook County's measure, assessment per square foot of building, is an example.

Market value compares your assessed market value with what similar homes actually sold for. It needs arm's-length sales from a period the board accepts.

Many appeals use both. They answer different questions, so keep them in separate tables.

Why choosing comps by price backfires

It's tempting to search for the lowest-assessed or cheapest-selling homes and call them comparable. Boards have the whole neighborhood's records, and a set that leaves out similar homes with higher values is easy to spot. Worse, if the comps aren't really similar (a smaller house, a different building class, a sale between relatives), the board can set them aside and your evidence is gone.

The safer approach is to fix the rule first and let the results fall where they may: decide what "similar" means before you look at any values, apply it to every home in the area, and keep the full list.

How our check chooses comparable homes

Property Appeal's check follows that approach and publishes its rules on the methodology page:

1. Hard filters first: same class code, same neighborhood, same number of units, the allowed sales window, and arm's-length sales only.
2. Similarity score: each remaining home is scored on size, age and other characteristics and on distance, never on its price or assessment.
3. Spread: only a limited number of homes may come from one block face.
4. Disclosure: if too few homes qualify, the filters are relaxed step by step, each step lowers the confidence score, and the step used is shown. The whole qualifying pool is listed next to the homes selected from it.

The result is a set of facts (where your assessment falls among similar homes) rather than an opinion of what your home is worth. You decide what to do with it.

A checklist for your own comps

• Same property type and class as yours, in your assessment neighborhood.
• Similar living area, age and construction; note every difference.
• For sales: dates inside the period the board accepts, and only open-market (arm's-length) sales.
• Use the identifiers the board asks for. In Cook County, Board of Review hearing documents may include the PINs of the homes you compare.
• Photos help: the Cook County Board of Review asks for a color photo of the front of your property taken within the last 12 months, dated on the back, and strongly encourages photos of the homes you compare.
• Keep the list of every home you considered, including the ones that didn't help you.