How to find comparable sales for free

What a board is actually asking for

An assessor values houses in bulk. A mass-appraisal model runs across a whole neighbourhood and produces a number for every parcel in it, and the model does not know that your kitchen is from 1994 or that the lot behind you was sold to a developer. Your appeal is the argument that for this particular parcel, the model landed above what the market actually paid for houses like yours.

The evidence for that argument is a short table: a handful of nearby sales, each divided by its living area to give a price per square foot, with the median applied to your own square footage. Three sales is the practical minimum, five is plenty, and eleven mediocre ones are worse than three good ones because the weak ones invite the board to throw out the set.

The five rules a comparable has to satisfy

Every one of these, at the same time. A sale that fails any of them will be discounted, and more importantly it will make your other comps look less considered.

• Same neighbourhood. Same subdivision if you can, and the same school attendance zone without exception. School boundaries move prices by more than most homeowners believe, and an assessor will point at a boundary before you finish your sentence.
• Within about ±20% of your square footage. Bigger houses sell for more in total and less per square foot. A 3,000 sq ft sale used against your 2,100 sq ft house looks helpful on total price and argues against you on the measure that matters.
• Sold within twelve months of the assessment date. Eighteen is often tolerated in a flat market; anything older invites an argument about market movement that you will lose, because the assessor has the whole market and you have four houses.
• Arm’s length. No foreclosures, no short sales, no estate or family transfers, no transfers between related entities, no builder closeouts, no sale of a house that was not openly marketed. These get struck, and they cost you credibility on the ones that were fine.
• Similar in age, style and storeys. A 1972 single-storey ranch is not comparable to a 2019 two-storey four streets away, whatever the arithmetic says. Similar condition too — if the comparable was renovated last year and yours has original bathrooms, that is an argument for you, but only if you raise it before the assessor does.

Where to get them, in order of usefulness

1. Your county assessor or appraisal district property search

Start here, always. Nearly every county in the United States publishes a searchable property record online — search by address, by owner, or by map. Each record shows the assessor’s own view of that parcel: living area, year built, bedroom and bathroom count, lot size, the assessed value history, and in disclosure states the sale price and date.

This is the source a board trusts most, for the simple reason that it is theirs. When your comps come off the assessor’s own records, the argument stops being about whether the data is right and becomes about what the data means — which is the argument you want to be having.

It is also where you check the record for your own house. Square footage, bedroom count, whether a basement is finished, whether a pool exists. Errors here are common and they are the easiest appeal there is: you are not arguing about value, you are pointing at a fact that is wrong. Do this first. It takes five minutes and it sometimes ends the matter.

2. The county GIS parcel viewer

Most counties publish a map-based parcel viewer alongside the property search. Click any house on the map and you get its record. This is far better than searching addresses one at a time, because it makes the neighbourhood visible — you can see which parcels back onto the arterial road, which are on the cul-de-sac, which have three times your lot. Comparability is a geographic question and a map answers geographic questions.

3. Recorded deeds at the county clerk or recorder

In disclosure states, the deed records carry the consideration paid. They are public, they are usually searchable online, and they are the primary source that the assessor’s own sale data is derived from. Slower to use than the property search, but definitive when a price is disputed.

4. Commercial listing sites

Redfin, Zillow, Realtor.com and their equivalents. Filter to recently sold, draw a boundary around your immediate neighbourhood, and constrain the square footage range. What these give you that the county does not is photographs and interior descriptions — which is how you find out whether a comparable had been renovated, and therefore whether it belongs in your table at all.

What they are not is evidence. Their square footage is often taken from listing copy rather than the county record, their sale dates can lag, and their automated valuations have no standing whatever with an appeals board. Use them to identify comparables, then pull the county record for each one and bring that.

5. An agent you already know

If you have bought or sold recently, the agent has MLS access and can send you a comps sheet in ten minutes. Most will do it without being asked twice. MLS data is more complete than anything public and is usually accepted as evidence, particularly where the printout carries the agent’s details.

What to do in a non-disclosure state

Twelve states do not require sale prices to be publicly recorded — Texas is the largest and the most consequential, with Kansas, Missouri, Mississippi, Louisiana, Alaska, Idaho, Montana, New Mexico, North Dakota, Utah and Wyoming alongside it. In those states you cannot look up what the house down the street sold for, and neither, officially, can the assessor.

So the argument changes shape. Instead of comparing your assessment to sale prices, you compare it to the assessor’s own values on comparable properties. That is a uniformity or equity argument rather than a market-value argument, and in Texas it is explicitly available and frequently the stronger of the two: if the appraisal district has your neighbour’s near-identical house at $172 per square foot and yours at $192, the district has to explain the difference. It is arguing with itself, using its own numbers, which is a good position for you to be standing in.

Practically: use the appraisal district’s property search exactly as above, but record each comparable’s assessed value per square foot rather than a sale price. Enter those into the calculator in the sale price field — the arithmetic is identical, and the median of assessed values per square foot is what you are asking to be assessed at. Say plainly in your protest that this is an equal-and-uniform argument. Where you do have real sale figures — your own recent purchase, a neighbour who volunteers theirs, a closing statement — those are still worth including.

Building the table

For each comparable, record: address, sale price or assessed value, living area, sale date, year built, and one line on why it is comparable. Then divide price by area for each one and take the median. Not the average — with three to five sales a single odd transaction drags an average badly, and the median is what an appraiser would use.

The appeal calculator does that arithmetic, checks each comparable against the ±20% size rule and the twelve-month window as you type, and prints a summary you can attach to the protest. Bring the county printout for every sale in the table. A board will not take your arithmetic on trust and it should not have to.

Before you spend an afternoon on any of this

Check your exemptions. A homestead exemption you are not receiving is worth more than most successful appeals, every year, permanently, and it requires one form and no hearing. Recent buyers are the usual casualties — the exemption generally does not transfer with the deed and nobody sends a reminder. Over-65, veteran and disability exemptions stack on top and are often larger again. The calculator flags this before it flags anything else, deliberately.