Tax assessed value and market value are two different numbers that answer two different questions about your home. Market value is what a willing buyer would pay in a normal sale today. Assessed value is the figure your local tax office assigns to your property for the sole purpose of calculating your property tax bill, and it’s usually lower than market value because most jurisdictions apply a fractional assessment ratio. A home worth $400,000 on the open market might carry an assessed value of $200,000 or $320,000, depending on where you live. Knowing which number governs which decision keeps you from overpaying taxes and prevents surprises when you sell, refinance, or insure the property.
What Market Value Actually Measures
Market value is the most probable price a property would bring in a sale between a willing buyer and a willing seller, with neither side under pressure. It moves with supply, demand, interest rates, and neighborhood trends, and it can change from month to month.
For a typical house, an appraiser arrives at market value by looking at recent sales of similar nearby homes and adjusting for differences in size, age, condition, and features. Newer or unusual properties may instead be valued by estimating what it would cost to rebuild the structure and adding land value. Rental and commercial buildings are usually valued from the income they produce. Outside forces shape the number too: school district quality, walkability, crime rates, proximity to employers, and mortgage rates all pull prices up or down independently of the building itself.
How Assessed Value Is Calculated
Your local assessor’s office sets assessed value using a formula, not a negotiation. The process usually starts with a mass appraisal of every property in the jurisdiction, using computer models fed by recent sales data, property characteristics, and neighborhood factors. The assessor then applies an assessment ratio to the estimated fair market value.
That ratio is the key. Some jurisdictions assess at 100% of market value, while others use ratios as low as 10% or as high as 50%. If your home’s fair market value is $400,000 and your jurisdiction uses a 50% assessment ratio, your assessed value is $200,000. That $200,000 is what the tax rate is applied to, not the market value. Comparing assessed values between counties or states without knowing the local ratio is misleading, because a $150,000 assessed value in one county can represent a more expensive home than a $250,000 assessed value in another.
Equalization Factors
Some states add a correction on top of the ratio. When an assessor’s office consistently values properties above or below the target ratio, the state applies an equalization multiplier to bring that district in line with neighboring areas. If a county is assessing homes at 28% of market value when the state requires 33.3%, every assessment in the county gets multiplied upward. The goal is fairness across jurisdictions that share taxing bodies like school districts.
Reassessment Cycles
Roughly 27 states reassess property values every year. The rest operate on cycles of two to six years, and some let local governments choose their own schedule within a statutory range. Between reassessments, your assessed value stays frozen at the last recorded figure regardless of what the market does. That lag is one of the biggest reasons the two values diverge.
From Assessed Value to the Tax Bill
Assessed value is one ingredient in your bill. The other is the tax rate, often expressed as a millage rate, where one mill equals $1 of tax for every $1,000 of assessed value. If your assessed value is $200,000 and the combined millage rate from all local taxing authorities is 30 mills, your ad valorem tax is $6,000. Multiple entities usually stack on a single bill: county, city or town, school district, library district, fire district. Two homes with identical assessed values in the same county can carry different tax bills if one sits inside city limits and the other doesn’t. Many bills also include flat non-ad valorem charges for things like stormwater, solid waste, or fire rescue, which is why the total may not match a simple millage calculation.
Why the Two Numbers Drift Apart
In a perfect system, assessed value would track market value at a consistent ratio. In practice, the two frequently move apart, sometimes by a wide margin. Three forces do most of the work.
Assessment Lag
A home reassessed three years ago reflects the market from three years ago. If prices rose 25% since then, the assessed value is stuck at the old number until the next cycle. The reverse also happens: in a downturn, you can end up paying taxes on a value higher than what your home would actually fetch. Owners in multi-year reassessment jurisdictions feel this the most.
Assessment Caps
Many states limit how much an assessed value can rise in a single year or cycle, even when market value jumps far more. California caps annual increases at 2% for properties that haven’t changed hands. Florida caps homestead assessment increases at 3%. New York and South Carolina prohibit increases above 20% and 15%, respectively, within a five-year period.1MOST Policy Initiative. Property Tax Assessment Limits These caps protect long-time owners from sudden tax spikes but widen the gap between assessed and market value over time. The cap typically resets when the property sells or is significantly renovated, so a new buyer often faces a much larger tax bill than the previous owner was paying.2Tax Foundation. Limiting Property Tax Bill Increases
Renovations and New Construction
Adding a garage, finishing a basement, or building a deck generally triggers an immediate reassessment of the improved portion, even outside the normal cycle. The assessor values the new work and adds it to the existing base. The market doesn’t always reward improvements dollar for dollar: a $40,000 kitchen remodel might add only $25,000 in resale value while the full cost shows up on your next assessment. Cosmetic upgrades that don’t require permits often go unnoticed by the assessor.
When Each Value Matters
The two numbers govern separate parts of homeownership. Confusing them causes real financial mistakes.
- Property taxes: only assessed value matters. Your bill is assessed value multiplied by the local millage rate. Market value is irrelevant to the tax collector.
- Selling your home: market value controls. Buyers and their lenders don’t care what the assessor says. The appraised market value determines what a bank will lend against the property and what the sale ultimately closes at.
- Refinancing or a home equity line of credit: the lender orders its own appraisal at market value. Your tax assessment has no bearing on how much equity the lender will recognize.
- Homeowners insurance: insurers base coverage on replacement cost, not assessed value. Insuring at the assessed figure would leave you drastically underinsured in most jurisdictions.
- Estate and gift tax: federal tax law uses fair market value at the date of death or transfer, not the local assessed value.
A low assessed value saves you money on taxes and tells you nothing about what your home is worth in a sale. Homeowners sometimes celebrate a low assessment without realizing it has no effect on their equity, borrowing power, or insurance needs.
Lowering the Assessed Value: Exemptions and Appeals
If the assessed value on your bill looks high, or you’ve never checked whether you qualify for relief, there are two levers to pull.
Homestead and Other Exemptions
More than 40 states offer some form of homestead exemption that reduces the taxable assessed value of a primary residence.3Institute on Taxation and Economic Policy. Property Tax Homestead Exemptions Exemptions come in two basic forms: flat dollar reductions that subtract a fixed amount from your assessed value, and percentage reductions that cut a share of the assessed value before the tax rate is applied. Eligibility almost always requires that you own and occupy the property as your primary residence.
Additional relief exists for specific groups. Senior citizens often qualify for larger exemptions or assessment freezes once they reach 62 or 65, sometimes with income limits. Disabled veterans and surviving spouses of service members killed in action frequently receive partial or full exemptions from property taxes. Some jurisdictions also offer circuit breaker credits that cap property taxes as a percentage of household income and refund or credit the excess to low- and moderate-income homeowners and renters.
Most exemptions require an application. They don’t happen automatically. If you’ve never filed for a homestead exemption you’re entitled to, you’ve been overpaying, and most jurisdictions won’t retroactively refund the difference. Check with your local assessor’s office as soon as you close on a primary residence.
Appealing the Assessment
If your assessed value looks too high relative to what your home would actually sell for, you can challenge it. National data suggests roughly 60% of property tax appeals result in a reduction.
Start by requesting your property record card from the assessor’s office. It shows the data behind the assessment: square footage, lot size, bedroom and bathroom counts, year built, and condition ratings. Factual errors are surprisingly common and are the easiest wins. If the records show four bedrooms and you have three, or 2,200 square feet when you have 1,950, that mistake alone could be inflating your bill.
For a value-based challenge, pull recent sales of comparable homes in your area, ideally similar in size, age, and condition and sold within the past year or two. A professional appraisal strengthens the case but costs roughly $450 to $1,500 for a residential property, so it makes sense only when the potential tax savings justify the expense over several years.
Every jurisdiction sets a filing deadline tied to the date you receive your assessment notice, typically 30 to 120 days. Miss the window and you’re locked in until the next cycle. In most states the assessor’s valuation carries a legal presumption of correctness, so the burden of proof is on you. Walking in and saying your taxes feel too high, without comparable sales or documented errors, rarely works. You also have to keep paying your property taxes on time while the appeal is pending; an open case doesn’t pause the obligation, and if you win you’ll receive a refund or credit.
What Happens If You Don’t Pay
Ignoring a property tax bill can eventually cost you the home. Unpaid taxes become delinquent on a jurisdiction-specific deadline, and penalties and interest start accruing immediately. Interest rates on delinquent property taxes range from about 1.5% to 18% annually depending on the state, and many jurisdictions add a one-time penalty of 3% to 20% on top of the unpaid balance.
If the taxes stay unpaid, the local government can place a tax lien on the property or sell the property at a tax sale. Some states sell the lien to private investors; others sell the deed outright. The process can begin within one to two years of delinquency. After a tax sale, most states give the former owner a redemption period to reclaim the property by paying the full delinquent amount plus interest, penalties, and costs, though the window can be as short as 30 days or as long as several years.
If you’re struggling to pay, contact the local tax office before the bill becomes delinquent. Most jurisdictions offer installment plans, and homeowners who qualify for exemptions or deferrals can sometimes reduce the balance. Waiting until a lien is filed makes every option more expensive.