Preparing a property tax assessment appeal
An assessment you disagree with is a research project with a deadline. Here is how the evidence works, with a made-up example.
The situation
I disagreed with an assessed value and used AI to prepare two packets: a request for an informal review, and a more formal evidence packet for an appeal. Rules and deadlines differ a lot between places, so this page stays generic and every number below is invented. As of writing, the county has not decided.
The concepts
- Assessed value is not your tax bill. The bill is roughly the assessed value times a rate. An appeal disputes the value. It does not argue about the rate.
- Market value on a specific date. Assessors value property as of a stated valuation date. Sales that happened long before or after that date are weaker evidence.
- The burden is usually on the owner. The assessment starts out presumed correct, so you need evidence, and the strongest evidence is recent sales of similar properties.
- Informal first, formal second. Many places let you ask the assessor to take another look before a formal filing. It is quicker and cheaper, but it does not stop the formal-appeal clock.
- Deadlines are hard. The window to file can be as short as a couple of months from the notice. Find yours from the assessor's own notice, not from a blog.
Comparable sales and adjustments
A comparable sale (a "comp") is a recent sale of a similar property nearby. Because no two properties match, you adjust each comp's sale price for the differences, then look at where the adjusted values cluster. That cluster is your opinion of value.
A comp-pull specification keeps the search honest. A typical one fixes the area (same neighborhood or a short radius), the property type, a size band (for example within about 15% of the subject), and a sale-date window around the valuation date. It records every comp that fits instead of picking the flattering ones.
A worked example
The subject is a made-up 1,800 square foot home assessed at $1,000,000. Say a size adjustment of $200 per square foot and a small allowance for condition or lot:
| Comp | Size | Sold for | Size adjustment | Other adjustment | Adjusted value |
|---|---|---|---|---|---|
| A | 1,750 sq ft | $905,000 | +$10,000 | -$5,000 (better condition) | $910,000 |
| B | 1,900 sq ft | $950,000 | -$20,000 | +$8,000 (smaller lot) | $938,000 |
| C | 1,820 sq ft | $925,000 | -$4,000 | none | $921,000 |
The adjusted values are $910,000, $938,000 and $921,000, with a median of $921,000 and a mean of $923,000. That supports an opinion of value of roughly $921,000, which is about $79,000 (8%) below the assessment.
Invented numbers. The green line is the opinion of value, the dashed line is the assessment.
Three comps is a minimum. More comps, and a tight spread among them, make a stronger case. A wide spread is a signal to find out why, not a number to average away.
The rule I held the AI to
I would not let the AI invent comparable sales. Search results and listing snippets often show an asking price instead of a sold price, the wrong date, or a nearby but different property, and a language model will happily fill the gaps with plausible-looking numbers. So the AI built the structure, the adjustment math and the writing, and every sale in the packet had to be checked against a real record: county sale records, the assessor's data, or listing-service sold data. When it could not source a comp, it said so instead of guessing.
What went into the packets
- Informal review: three sold comps, an opinion of value, short submission text, a checklist and the deadlines.
- Formal appeal: the same evidence organized as exhibits, the procedural rules, what to expect at a hearing, and the comp-pull specification so another person could repeat the search.
Where it stands
Both packets are done and the formal appeal is filed. The county has not decided. The useful part of the exercise is that the work was built to be checked: each number traces back to a record, and each adjustment is written down.
I'm not a tax professional or an appraiser. Rules, deadlines and the standard of proof vary by place, so read your own assessor's notice and consider a local professional for a large dispute.
This is entry 16 of AI Lab Work.