Property tax: how it is calculated and how to challenge it

Property tax is the largest recurring cost of owning a home after the mortgage, and it is calculated in a way most owners never examine. It is worth ten minutes, because the input most likely to be wrong is the one you can challenge.

The calculation

Tax equals assessed value × assessment ratio × millage rate, less any exemptions. Three of those four vary by jurisdiction and one of them is an opinion.

• Assessed value is the assessor's estimate of your property's value. It is not necessarily market value and it is not necessarily current.
• Assessment ratio is the share of assessed value that is taxable. Some states tax the full amount; others tax a fraction.
• Millage rate is the tax per thousand dollars of taxable value, set by whichever bodies levy against your parcel: county, city, school district, and often special districts.
• Exemptions reduce the taxable amount. Homestead, senior, veteran, disability and agricultural exemptions are all common and all under-claimed.

Why statewide comparisons mislead

Effective rates are usually quoted statewide, which is fine for comparing states and close to useless for budgeting. The spread between two counties in the same state routinely exceeds the spread between two states, because school district levies dominate the total and they are local.

Two identical houses ten miles apart, in different districts, can carry annual bills differing by thousands. Never rely on a state average when the number matters; get the actual millage for the specific parcel.

Why your assessment is often wrong

Assessors value thousands of properties with limited resources and rarely enter any of them. Errors are routine and systematic:

• Stale valuations. Many jurisdictions reassess on a multi-year cycle. Between cycles your assessment reflects an older market, which cuts both ways.
• Wrong physical facts. Recorded square footage, bedroom count, lot size, and finished basement status are frequently wrong. This is the most winnable category of appeal because it is objective.
• Condition unseen. The assessor has not seen your failing roof or your unrenovated interior, and has assumed average condition for the area.
• Bad comparables. Automated mass appraisal may compare your property with ones that are not genuinely similar.

How to appeal, and what actually works

Appeals succeed on evidence about value or facts, and fail on arguments about fairness or affordability. The board cannot help with the latter.

1. Get your property record card. It is public. Read every field. Wrong square footage is the single most common and most winnable error.
2. Check comparable assessments, not just sale prices. If similar neighbouring homes are assessed lower, that is a uniformity argument and in many jurisdictions it is the strongest one available.
3. Gather recent comparable sales that closed below your assessment, genuinely similar in size, age and location.
4. Document condition with photographs and contractor quotes if there are real defects.
5. File within the window. Deadlines are short, often 30 to 60 days from the notice, and they are enforced absolutely. Miss it and you wait a year regardless of how strong your case is.

Most appeals are informal at first and cost nothing but time. Where an appeal is worth thousands a year, and property tax recurs forever, a professional representative on contingency can make sense.

Two things to do regardless

Check you are receiving every exemption you qualify for; they are not applied automatically and homestead exemptions in particular go unclaimed for years. And check the assessment every cycle rather than only when the bill jumps, because an error compounds quietly for as long as nobody looks.