Your property tax bill equals your assessed value times an assessment ratio times the local millage rate. To appeal, you file a written challenge within your jurisdiction’s deadline, which commonly runs 30 to 60 days from the date on your notice, and you support it with comparable sales or an independent appraisal showing the assessor’s market value is too high. Nothing else you argue matters much.
That last point is where most homeowners lose. The board hearing your property tax assessment appeal almost never has power over the tax rate, the school budget, or how much your neighbor pays. It has power over one number: the estimated market value of your parcel. Everything below works through that number with real arithmetic.
How assessors calculate your property tax bill
Three inputs produce the figure on your bill.
Market value estimate. The assessor’s opinion of what your property would sell for as of a specific valuation date (January 1 in many states). This is the only input an appeal usually touches.
Assessment ratio. The percentage of market value that is legally taxable. It is not always 100%. In Illinois, for example, state law sets the statutory assessment level at 33 1/3 percent of market value outside of Cook County, while Cook County’s classification ordinance assesses residential property at 10 percent and commercial at 25 percent. Georgia uses 40%. Washington and several others tax at full market value. The ratio is set by statute or county ordinance, and you cannot appeal it.
Millage rate. Tax per $1,000 of assessed value. One mill is $1 per $1,000, so 25 mills equals 2.5% of assessed value. Maryland and a few other states quote the same thing per $100 instead, so a 1.1% rate appears as $1.10. Converting to a decimal before you multiply avoids an order-of-magnitude error.
The formula:
- Assessed Value = Market Value x Assessment Ratio
- Tax Bill = Assessed Value x Millage Rate (minus any exemptions applied to the assessed value first)
Illinois adds one more step worth knowing if you live there. The state applies a county equalization factor so that, in aggregate, assessments reach the 33 1/3 percent level required by statute, which is why a Cook County bill shows an "equalized assessed value" well above 10% of market value.
The practical reason appeals succeed is the valuation method. Assessors value thousands of parcels at once using mass appraisal models built on sales data, square footage, lot size, and neighborhood codes, not individual walkthroughs. A model that has your 1,850-square-foot house recorded at 2,200 square feet will produce a confidently wrong number every year until somebody corrects the record. This is also how an assessment differs from an appraisal or inspection, which look at one property in detail.
Worked example: from assessed value to tax bill to a lower bill after appeal
Take a home the assessor values at $340,000, in a jurisdiction with a 40% assessment ratio and a 25-mill rate.
Before the appeal
| Line | Calculation | Result |
|---|---|---|
| Assessor’s market value | given | $340,000 |
| Assessment ratio | x 40% | $136,000 assessed |
| Millage rate | x 25 mills (0.025) | $3,400 tax bill |
Now the homeowner pulls three recent sales from the assessor’s own public records: a 1,900-square-foot ranch two streets over at $295,000, a nearly identical floor plan in the same subdivision at $302,000, and a slightly larger house with an updated kitchen at $312,000. All three sold within the past nine months. Adjusted for size and condition, they point to a market value near $300,000 rather than $340,000.
After the board accepts $300,000
| Line | Calculation | Result |
|---|---|---|
| Corrected market value | from comparable sales | $300,000 |
| Assessment ratio | x 40% | $120,000 assessed |
| Millage rate | x 25 mills (0.025) | $3,000 tax bill |
The reduction is $400 a year, or 11.8%. Notice that the percentage cut in the tax bill is exactly the percentage cut in market value: 40,000 / 340,000 = 11.8%. That proportionality is the single most useful thing to understand before you file, because it lets you price the effort in advance. Multiply your current bill by the percentage you think the value is inflated, and you have your maximum realistic savings. A homeowner convinced the assessor is 5% high on a $2,800 bill is chasing $140.
Two caveats on that math. The ratio and the millage rate are unchanged in both columns because an appeal cannot move them. And if your jurisdiction phases in increases or caps annual growth in taxable value, the first-year saving can be smaller than the full-value reduction implies, since the capped figure may already sit below the assessor’s new number.
Step-by-step: how to actually file and win an appeal
- Find your deadline on the notice itself. It is printed there, and it is short. Maryland requires appeals within 45 days of the notice date. King County, Washington, sets the deadline at the later of July 1 of the assessment year or 60 days from the mailing date on the value notice. In Texas, the protest deadline is May 15 or 30 days after the appraisal district mails the notice, whichever is later, counted from the mailing date rather than the day it lands in your mailbox.
- Check the property record card for factual errors. Request it from the assessor’s office; it is public. Square footage, bedroom and bathroom counts, lot size, year built, finished basement, garage stalls, pool. A single wrong field can move a mass appraisal model by tens of thousands of dollars, and errors of fact are the easiest category of appeal to win because no judgment is involved.
- Build a comparable sales set. Three to six arms-length sales, close to the valuation date, in your neighborhood, similar in size, age, and condition. Many assessors publish the sales data they used, and Maryland explicitly provides a property worksheet and an area sales listing at no cost before the hearing. Starting from the assessor’s own data set is more persuasive than importing listing prices from a real estate portal.
- File in writing, within the window, with the right body. That is the Supervisor of Assessments in Maryland, the county appraisal review board in Texas, the Board of Equalization in Washington counties, and the local Board of Assessment Review in most of New York. State the value you believe is correct and the specific reasons, not just that the number feels high.
- Present evidence at the hearing or in writing. Hearings are informal and short. In an estimated 80% of US jurisdictions the burden of proof sits with the owner rather than the assessor, according to analysis reported by Bankrate, meaning you have to affirmatively show the figure is wrong. Watch the evidence-exchange rules: King County requires submissions at least 21 business days before the hearing date.
- Read the decision and note the next deadline. Partial reductions are common. If you are dissatisfied, there is almost always a second and third tier. Maryland’s path runs from the supervisor’s level to the county Property Tax Assessment Appeal Board within 30 days, then to the Maryland Tax Court, which hears the case de novo. Washington appeals go to the state Board of Tax Appeals; Texas offers district court or, for qualifying properties, binding arbitration.
Appeal windows and success rates by state
| Jurisdiction | Typical filing deadline | First-level body | If denied |
|---|---|---|---|
| Maryland | 45 days from notice date | Supervisor of Assessments (SDAT) | PTAAB within 30 days, then Maryland Tax Court within 30 days |
| Texas | May 15, or 30 days after notice is mailed, whichever is later | County appraisal review board (ARB) | District court, binding arbitration, or SOAH |
| King County, WA | Later of July 1 or 60 days from notice mailing | County Board of Equalization | Washington State Board of Tax Appeals, generally 30 days |
| New York (most towns) | Grievance Day, usually the fourth Tuesday in May | Board of Assessment Review (Form RP-524) | Small Claims Assessment Review or state Supreme Court |
| Illinois | Set by each county board of review; confirm the published date | County board of review | Illinois Property Tax Appeal Board or circuit court |
New York’s deadline has more exceptions than any other in the table. Grievance Day is the fourth Tuesday in May in most communities, but New York City requires Class One complaints by March 15 and Nassau County by March 1, and towns sharing an assessor can set dates as late as the second Tuesday in June.
On how many homes are overvalued, the most widely cited figure comes from the National Taxpayers Union Foundation: an estimated 30% to 60% of US properties are overassessed, while fewer than 5% of owners appeal. Treat the top of that range as an advocacy estimate rather than a measurement; it is a wide band for a reason, and the organization that produced it campaigns for lower taxes.
Published success rates disagree, and the disagreement is informative. NTU has put the share of challengers who win at 20% to 40%, while secondary summaries of IAAO and Lincoln Institute of Land Policy research place the national range at 40% to 60% (that source sells appeal services, so weigh it accordingly). The spread largely reflects what gets counted. Jurisdictions where most protests settle informally with the assessor before a formal hearing report high win rates; boards that only tally contested hearings report lower ones. Either way, the gap between documented appeals and unsupported complaints is bigger than the gap between states. The president of the NTU has described the need for "solid proof" once your assessment diverges roughly 10% or more from comparable per-square-foot assessments.
One structural point: lowering your assessment does not lower the total amount your taxing districts need to collect. Levies are set separately, through the same kind of public process that governs how local rate increases get approved, which is why a successful appeal shifts your share of the burden rather than shrinking the pie.
Common mistakes that get appeals rejected
Arguing about the bill instead of the value. "My taxes went up 14%" is not a ground for appeal. Boards review valuation, and in New York the enumerated grounds are that the assessment is excessive, unequal, unlawful, or that the property is misclassified. Rate complaints belong at budget hearings.
Missing the deadline. This is a hard cutoff nearly everywhere. Under New York law, failing to file on time forfeits both administrative and judicial review of that year’s assessment. Late filings in Washington are accepted only under narrow conditions.
Using comparables that are not comparable. Sales from a different school district, a different lot size class, or a different condition tier get discounted or dismissed. Distressed and family-transfer sales are not arms-length. Three tight comparables beat ten loose ones.
Assuming your purchase price settles it. It often does not. Because many jurisdictions apply a fractional assessment and value as of a fixed date, a sale price is treated as one piece of market evidence, not as a substitute for the assessed value. If you bought below the assessor’s figure, document the transaction and support it with comparables anyway.
Appealing a value that is already correct. Run the proportionality math first. If your evidence supports a 3% reduction, the hearing may not be worth a day off work.
Frequently asked questions
Can appealing cause my assessment to go up? Boards generally have authority to confirm, lower, or raise the value under review, and some states allow the assessor to appeal the board’s decision too. In practice an increase is uncommon when the filing is supported by solid comparables, but it is not structurally impossible, which is a reason to check your own comparables honestly before filing.
Do I need a lawyer? Not for a first-level residential appeal. These hearings are designed for self-representation, and New York’s guidance notes you may appear personally with or without a representative. Attorneys and consultants become more relevant at judicial tiers and for commercial property.
When do I see the savings? Usually on the following year’s bill, because the assessment year precedes the tax year. King County states plainly that the assessment determines taxes payable in the following year; if you have already paid, a reduction can come back as a revised statement or refund.
Is there a filing fee? Administrative appeals are typically free. Maryland’s supervisor’s-level and PTAAB stages charge nothing, and Texas protests and Washington board petitions carry no filing fee. Judicial and small-claims tiers are where fees appear, such as New York’s Small Claims Assessment Review, so confirm costs with your own jurisdiction before escalating.
A reasonable filter before you commit: pull your property record card, fix any factual error first since that is the highest-probability win, then estimate the percentage your value is inflated and multiply it by your current bill. If that number clears a few hundred dollars a year and you have three genuinely similar sales to show for it, the paperwork pays for itself. Rules and deadlines vary by county and change, so verify the specifics with your assessor’s office or a qualified tax professional before filing.