How this is calculated
Assessors value in bulk. They run a model across a whole neighbourhood, and the model does not know that your kitchen is original or that the house behind you backs onto a highway. An appeal is the process of showing that, for your specific parcel, the model landed above what the market actually paid.
The standard residential evidence is a dollars-per-square-foot comparison. Divide each comparable sale by its living area, take the median of those figures, and multiply by your own living area. The median rather than the average, because with three to five sales a single odd transaction would drag an average badly.
The tax saved is the reduction in value, multiplied by your assessment ratio, multiplied by your tax rate — and then multiplied by the number of years the reduction survives before the next general reassessment resets it. That last number is the one people forget, and it is usually the difference between “not worth the afternoon” and “worth the afternoon.”
Worked example. A notice values the home at $412,000. The living area is 2,150 sq ft, so the assessor is at $191.63 per square foot.
Three sales nearby: $358,000 ÷ 2,040 = $175.49; $372,500 ÷ 2,210 = $168.55; $389,000 ÷ 2,260 = $172.12. The median is $172.12, and 172.12 × 2,150 = $370,066.
The assessment is $41,934 — 11.3% — above what the comps indicate. At a 100% assessment ratio and a 2.00% tax rate that is $838.67 a year. Over three years, $2,516. A firm keeping 40% of it would leave you $1,510, so on this one you file it yourself.
How to pick comparable sales that a board will accept
This is the part that stops people, so here is the whole rule set. A comparable sale has to be all of these things at once:
- Same neighbourhood. Ideally the same subdivision, and the same school attendance zone — school boundaries move prices more than most people expect.
- Within roughly ±20% of your square footage. Larger homes sell for more in total and less per square foot, so a comp far outside your size range argues against you even when the total price looks helpful.
- Sold in the last twelve months. Most boards will take up to eighteen months in a slow market, but the closer to the assessment date, the better.
- Arm’s length. No foreclosures, no estate or family transfers, no builder closeouts, no sales between related parties. These get thrown out and they cost you credibility for the comps that were fine.
- Similar in age, style and storeys. A 1972 ranch is not comparable to a 2019 two-storey four blocks away, whatever the price per foot says.
Where to get them, free: your county assessor or appraisal district has a public property search that shows sales, square footage and the assessor’s own record for every parcel — that is the source a board trusts most, because it is theirs. The county GIS parcel viewer lets you click neighbouring properties directly on a map. Recorded deeds at the county clerk give sale prices in states that disclose them. Redfin and Zillow sold filters are useful for photographs and floor area, but bring the county printout to the hearing. In the twelve non-disclosure states — Texas among them — sale prices are not public record, so use the assessor’s own values on comparable homes instead of sale prices, which is exactly what the appraisal district will be doing.
Full walkthrough: how to find comparable sales for free.
Check your exemptions before you check your comps
A homestead exemption removes a fixed amount from taxable value every year, for as long as you live there, with no hearing and no evidence. In the worked example above it is worth $800 a year — very nearly what winning the whole appeal is worth, and it does not reset at the next reassessment.
People miss them constantly, and recent buyers miss them almost as a rule: the exemption usually does not transfer with the property, and nobody sends a reminder. Over-65, veteran and disability exemptions stack on top and are frequently larger. If Plate III says you might be missing one, deal with that first — it is one form.
What this does not account for
- Adjustments between comps. A real appraiser adjusts each sale for lot size, garage bays, pools, condition and time. This tool compares raw dollars per square foot, which is what most residential boards work from, but a well-adjusted grid beats it.
- Caps and phase-ins. Texas’s 10% homestead cap, Florida’s Save Our Homes, Michigan’s taxable-value cap and California’s Proposition 13 base all mean your taxable value may already be far below market — in which case a market-value reduction saves you nothing at all until the capped value catches up.
- Equity or uniformity appeals. Several states let you argue that you are assessed unequally against similar properties even when the market value is right. In Texas that is often the stronger argument.
- Whether the board agrees. This models a full reduction to the indicated value. Boards commonly split the difference.
- Your time. Two to six hours for a first appeal, most of it gathering comps.
- Rates changing. Taxing units set rates annually. A reduction in value can be partly offset by a rate rise, and that is outside anyone’s control.
Common questions
How much over do I need to be before it is worth filing?
As a rule of thumb, 5% or more on value, and a reduction you expect to hold for at least two years. Below that, boards rarely move and the arithmetic stops justifying the afternoon. The calculator shows you the actual dollars rather than the rule of thumb, which is better.
Can they raise my assessment because I appealed?
In some jurisdictions a board can increase an assessment it believes is too low. It is uncommon on residential property, but it is a real reason not to file when your own comps do not support a reduction. If the tool says you are assessed below your comps, take that seriously.
Do I need an appraisal?
Usually not for a residential appeal. An independent appraisal costs $350–$600 and is worth it when the gap is large, the property is unusual, or an informal review has already failed. Enter it in the cost field and see whether it still pays.
What is the difference between assessed value and market value?
Market value is what the assessor thinks the property would sell for. Assessed or taxable value is the portion of that which is actually taxed, after the assessment ratio and any exemptions. In some states they are the same number; in Ohio, Georgia, Michigan and Illinois they are not, and mixing them up will give you an answer that is wrong by a factor of two or three.
Should I take the informal review first?
Yes, where one is offered. Most assessors will meet informally before the formal hearing, most reductions happen there, and it costs you nothing. File the formal protest anyway so the deadline is protected — you can always withdraw it.
Is a contingency firm ever worth it?
On commercial property, on complex valuations, and — honestly — when the alternative is that you never file. A firm keeping 40% of $2,516 leaves you $1,510, and $1,510 beats the $0 you get by not filing. What it does not beat is the $2,516 you keep by spending an afternoon on it.
Do I have to give anyone my address to use this?
No. Nothing here is transmitted anywhere — the arithmetic runs in your browser. The reason the funded competitors ask for your address and parcel number is that you are the product, not the calculation.