Assessed valuation is the dollar value your local tax assessor assigns to your property, and it is the figure the tax rate gets multiplied against to produce your annual property tax bill. In most places it equals a set percentage of your property’s estimated market value, though that percentage, called the assessment ratio, varies widely by state and locality. Because the number directly controls what you owe, an error in it costs you real money every year it goes uncorrected.
Assessed Value Is Not Market Value or Appraised Value
Three different numbers get thrown around when people talk about what a home is worth, and mixing them up is where most property tax confusion starts.
Market value is what a willing buyer would pay in a normal sale. Appraised value is a licensed appraiser’s professional opinion of that market value, typically produced for a mortgage lender during a purchase or refinance. Assessed value is what your local government uses to calculate your tax bill, and it may sit well below either of the other two.
The gap usually comes from the assessment ratio. If your home would sell for $400,000 and your jurisdiction uses a 50% ratio, your assessed value is $200,000, and $200,000 is what the tax rate gets applied to. Some jurisdictions assess at full market value; others assess at as little as 10%. The ratio is set by state law or local ordinance and applies uniformly to all properties in the jurisdiction. When an assessed value looks strangely low compared to what a house would sell for, the ratio is almost always the reason.
How the Assessor Arrives at the Number
The core formula is simple: the assessor estimates your property’s market value, then multiplies by the local assessment ratio. Building the market value estimate is where the real work happens.
Assessors lean primarily on the sales comparison approach, looking at recent sale prices of similar homes in your area. They factor in square footage, lot size, number of bedrooms and bathrooms, age of the structure, and the condition of major systems like the roof and HVAC. Then they adjust for differences between your property and the comparable sales. A home with a finished basement gets a higher value than an otherwise identical home without one.
How often the number gets refreshed depends on where you live. Some states require annual reassessments. Others operate on cycles of two to five years, and a handful allow gaps of up to ten years. In states with longer cycles, the assessed value can drift meaningfully away from actual market conditions in either direction. Several states also cap how much the assessed value can increase in a single year, regardless of what the market does. These caps protect homeowners from sudden spikes, but they can create wide gaps between assessed and market value over time, especially in fast-appreciating neighborhoods.
What Triggers a Reassessment Outside the Normal Cycle
Two events commonly force a fresh look at your property between scheduled reassessments.
The first is a change of ownership. When you buy a home, the assessor typically resets the assessed value to reflect the purchase price. If the previous owner benefited from years of capped increases, the new number after a sale can jump sharply. Buyers in states with assessment caps are sometimes surprised by a first-year tax bill that runs well above what the seller was paying.
The second is major construction. When you pull a permit for an addition, a full kitchen remodel, or a new structure on the property, the assessor gets notified. Routine maintenance like painting, replacing carpet, or swapping fixtures generally does not trigger reassessment. The line falls at work that adds square footage, changes the property’s use, or amounts to a major rehabilitation. When construction does trigger reassessment, the assessor values only the new work and adds it to the existing assessed value rather than reappraising the whole property.
Zoning changes and subdivisions can also prompt a reassessment. Rezone from residential to commercial, or split a parcel, and the assessor will reevaluate based on the new permitted use.
Turning Assessed Value Into a Tax Bill
The assessed value is the starting point, not the end. From there, the assessor subtracts any exemptions you qualify for to produce your taxable value. The local tax rate is then applied to that taxable value.
Most jurisdictions express the rate in mills, where one mill equals one dollar of tax per $1,000 of taxable value. If your taxable value is $300,000 and the combined millage rate is 15, your annual bill is $4,500. The millage rate is set by local taxing authorities, including school districts, municipalities, and counties, each of which may levy its own share. Voters often approve or reject proposed changes through ballot measures, so the rate can shift from year to year even when your assessed value doesn’t move.
Exemptions are where many homeowners leave money on the table. The most common is the homestead exemption, which reduces the taxable value of your primary residence by a fixed dollar amount or percentage. It is rarely automatic. In most jurisdictions you have to file an application with the county assessor or tax office, and there is a deadline. Some jurisdictions allow retroactive claims for a limited number of prior years, but not all do. Senior citizen exemptions typically kick in at age 65 and sometimes carry income limits, and can take the form of a reduced taxable value, a freeze on the assessed value, or a direct credit against the bill. Disabled veterans with a permanent service-connected disability often qualify for significant exemptions that scale with the disability rating; at a 100% rating, many states exempt a substantial portion of the home’s assessed value from taxation entirely. Surviving spouses of qualifying veterans may also be eligible.
Check the Assessor’s Records Before Anything Else
Before considering an appeal, verify that the assessor’s records on your property are accurate. Your assessed value is public information. Most county assessors post property records on their websites, searchable by address or parcel number, and the current assessed value also appears on your annual assessment notice and property tax bill.
Request your property record card from the assessor’s office, online or in person. This document lists the detailed data the assessor used: square footage, lot size, number of rooms, age of the structure, and any improvements. Errors here are surprisingly common. An extra bedroom, overstated square footage, or a finished basement that doesn’t actually exist can inflate the assessment by thousands of dollars, and data-entry mistakes can be carried forward for years without anyone catching them.
Compare the record card against what you know about the property. If you recently bought the home, your inspection report is a useful cross-reference. Pay particular attention to the condition rating the assessor assigned. A home rated “excellent” that actually has a 20-year-old roof and aging mechanicals is being overvalued relative to its true condition.
Filing an Appeal
Every jurisdiction sets a strict deadline for appealing an assessment. Most fall within 25 to 45 days after the assessment notice is mailed, though some use fixed annual dates. The deadline is almost always printed on the notice itself. There is generally no grace period and no exception for not having received the notice. Miss it and you are stuck with that valuation for the entire tax year.
The appeal is filed with your local board of review, assessment appeals board, or equivalent body. Some jurisdictions offer online portals; others require paper forms. Many charge a filing fee, typically under $200, though some boards accept appeals at no cost. The form will ask for your parcel identification number, the current assessed value, the value you believe is correct, and the basis for your claim.
The burden of proof falls on you. The assessor’s valuation is presumed correct, and in most jurisdictions you need to show by a preponderance of evidence that it is too high. Feeling that your taxes are unfair does not meet that bar. What does:
- Comparable sales data. Three to five recent sales of similar homes in your area that closed for less than your assessed value, chosen for similarity in square footage, lot size, age, and location. Proximity matters. A sale two blocks away is more persuasive than one across town.
- Factual errors in the property record card, documented and highlighted.
- An independent appraisal. A residential appraisal for tax appeal purposes typically costs $300 to $600 for a standard single-family home. It carries significant weight with appeal boards, but only makes sense if the potential tax savings justify the cost.
After filing you’ll receive notice of a hearing where you present your evidence to a panel or hearing officer, and the assessor’s office presents its side. Most boards issue a written decision within a few weeks to a couple of months. A successful appeal produces a revised tax bill, and some jurisdictions refund any overpayment. If the appeal fails, most states allow a further appeal to a state-level board or court, though cost and complexity climb sharply at that stage.
Because the tax bill depends on both the assessed value and the millage rate, a successful appeal only controls half the picture. A 10% cut in your assessed value saves you 10% on the bill, but a millage increase the next year can absorb the gain. Tracking both numbers year to year gives you a clearer read on where your money is going.
The Federal Deduction Angle
Property taxes on your home are deductible on your federal return if you itemize. A cap limits how much you can deduct. For tax year 2026, the total deduction for state and local taxes combined, including property taxes, state income taxes, and sales taxes, cannot exceed $40,400 for single and joint filers, with married-filing-separately limited to half that. The cap increases by 1% annually through 2029 and is scheduled to drop back to $10,000 beginning in 2030.1Office of the Law Revision Counsel. 26 USC 164 – Taxes
If your combined state and local taxes already run above the cap, cutting your property tax bill will not change your federal deduction. If your total sits at or below the cap, every dollar of property tax savings also reduces federal taxable income. That math is worth running before you decide whether an appeal is worth your time.