How property taxes are assessed: the complete guide

Last updated 2026-07-09

What does it mean to assess property taxes?

Assessing property taxes means a government official, usually the county assessor or appraiser, estimates the value of your property so the local taxing authority knows how much to charge you. That estimate is the assessed value. Your bill flows straight from it.

The chain has three links. The assessor sets a value. A second number, the assessment ratio, converts that value into a taxable base. Then a mill rate turns that base into dollars. Change any one of the three and your bill changes. Most homeowners only ever see the final number, which is why the whole thing feels like a black box. It isn't.

Property tax is the largest single source of revenue for local government in the United States. The Lincoln Institute of Land Policy reports that property taxes generated roughly $630 billion for state and local governments in fiscal year 2021 ^[1]. Your assessment is the machine that splits that load across every parcel in the jurisdiction. If your slice is bigger than it should be, someone else's is smaller.

How do assessors calculate your property's value?

Assessors use three approaches to value, all borrowed from the appraisal profession: sales comparison, cost, and income. For owner-occupied homes the sales comparison approach does the heavy lifting. The assessor finds recent sales of similar homes nearby and adjusts for differences in size, age, condition, and features.

The cost approach asks a different question. What would it cost to rebuild this structure from scratch today, minus depreciation, plus the land? It shows up most for new construction, odd properties, and anything that rarely trades hands. The income approach is the standard for commercial and rental property: you take the expected net income and capitalize it into a value. A single-family rental valued under the income approach can look very different from the identical house valued under sales comparison, which is one reason owners of small rentals sometimes get strange results ^[2].

Most residential systems don't send a live appraiser to your door every year. They run computer-assisted mass appraisal (CAMA) models that update thousands of parcels at once with statistics. The International Association of Assessing Officers (IAAO) sets the standards for these models, including a requirement that the median ratio of assessed value to sale price stay within 10% of the jurisdiction's stated assessment level ^[3]. Here's the catch. When a CAMA model is wrong, it's wrong at scale. That is how a whole neighborhood ends up overassessed on the same day.

What is an assessment ratio and why does it matter?

The assessment ratio is the slice of market value that becomes your taxable base. A $400,000 home in a state with a 50% ratio has an assessed value of $200,000. The mill rate hits that $200,000, not the full $400,000.

Ratios swing hard from state to state. Some assess at 100% of market value (California uses full cash value as the base, though Proposition 13 caps annual increases at 2% ^[4]). Others use fractions. Illinois assesses most residential property at 33.33% of market value ^[5]. Mississippi's residential ratio is 10%. Comparing raw assessed values across state lines tells you almost nothing.

Here's why this matters for your appeal. Say your assessor claims your home is worth $500,000 but comparable sales top out at $420,000. The overassessment is $80,000 in market value. At a 50% ratio that inflates your taxable base by $40,000. At a 30 mill rate ($30 per $1,000 of assessed value), you're overpaying $1,200 a year. Find and document that gap, and you've built the spine of an appeal.

State	Residential Assessment Ratio	Notes
California	~100% of purchase price	Prop 13 caps annual growth at 2% [4]
Illinois	33.33%	Cook County runs its own schedule [5]
New York	Varies by county	NYC uses 6% for Class 1 [6]
Texas	100% of market value	Homestead cap limits taxable value growth [7]
Florida	100% of just value	Save Our Homes caps homestead growth at 3% [8]
Mississippi	10% residential	One of the lowest ratios in the country

How is the mill rate set, and who controls it?

The mill rate (also called the millage or levy rate) is set by local taxing bodies, not the assessor. Schools, counties, cities, water districts, fire districts, and hospital districts each pass their own levies. One mill equals $1 of tax per $1,000 of assessed value. Your bill is the sum of every overlapping levy that lands on your parcel.

A 25 mill rate on a $200,000 assessed value gives you a $5,000 bill: $200,000 divided by 1,000, times 25. The assessor controls none of that math once the value is set. That split matters, because assessors and elected officials love to point at each other when budgets get tense.

Mill rates move as assessed values shift across the whole tax base. When values rise evenly, many jurisdictions cut the mill rate to hold total revenue flat (call it revenue neutrality, or the rollback rate). Texas law requires each jurisdiction to publish a "no-new-revenue" rate every year so voters can see whether they're really getting a tax hike ^[7]. But when your property rises faster than the average, your share of the total levy grows even if the mill rate drops. That is the quiet way overassessment picks your pocket.

For how this plays out in specific high-tax markets, see our breakdowns of nyc property tax and la county property tax.

When does the assessor revalue your property?

Revaluation cycles vary by state, and sometimes by county inside a state. Some places reassess every year. Others do a full revaluation every four years and adjust by a percentage in between. A few still run on irregular cycles and go a decade without a full reappraisal, which produces wildly stale values in both directions.

The IAAO's Standard on Mass Appraisal of Real Property recommends annual reassessment, or at minimum a cycle short enough to keep the median ratio inside acceptable bounds ^[3]. When a jurisdiction falls years behind and then catches up in one giant revaluation, homeowners get sticker shock that feels like a tax hike. Technically it's a correction to market value. The sticker shock is real either way.

The calendar drives your appeal rights too. Most states tie the appeal deadline to the date the assessment notice mails, not the date the tax bill arrives. Those two dates can sit six months apart. Miss the notice, miss the window. Typical deadlines run 30 to 90 days from notice mailing, though some jurisdictions give as few as 20 days ^[9]. Read your state's statute directly.

For county-specific deadlines and procedures, our guides to collin county property tax and williamson county property tax cover fast-growing Texas markets where reassessments have jumped sharply.

What data does the assessor use, and can you see it?

Assessors build their models on recorded sales data (deeds and transfer declarations), building permits, aerial and street-level imagery, prior assessments, and field inspection notes. In most states this data is public record, and you have a legal right to see the property record card for your parcel ^[10].

The property record card is where the money hides. It lists what the assessor believes about your home: square footage, bedroom and bathroom count, finished basement, deck, pool, HVAC type, effective age, condition grade. Errors are common. A finished basement recorded as unfinished. A two-car garage counted as three. A condition grade nobody has touched since a 1980s inspection. Each mistake inflates your value and costs you on every bill until you fix it.

Request the card online (most counties post parcel data on a GIS or assessment portal) or in person at the assessor's office. Then check every field against your actual house. Find a factual error and you often skip the formal appeal entirely: a correction request can adjust the value administratively. That route is faster and it costs nothing.

For Bay Area homeowners, the santa clara property tax and san mateo county property tax guides explain how to pull parcel data from those portals.

How do you know if your assessment is too high?

The test is short. Divide your assessed value by the local assessment ratio to get the assessor's implied market value. Then pull three to five real comparable sales from the six to twelve months before your assessment date.

If the comparables land consistently below the assessor's implied market value, you have a case. If they cluster right at or above it, you probably don't, and filing anyway wastes your time and the board's.

Sales data lives on your county assessor's website, in the local MLS (ask an agent to run a basic comp report), or in free tools like Zillow's "recently sold" filter and Redfin's search. None of those replace a formal appraisal. They're plenty accurate to tell you whether an appeal is worth chasing before you spend a dollar.

The gap between assessed market value and true market value is the assessment-to-sale ratio. A Lincoln Institute analysis of 2021 data found that in many major U.S. cities, lower-value homes carried higher assessment ratios than higher-value homes, meaning lower-income owners are systematically overcharged relative to what their homes are worth ^[1]. If you own a modestly priced home in a city with known regressivity, your odds of being overassessed run higher than average.

For a DIY framework to build that comparable case without hiring a contingency firm, the TaxFightBack appeal kit walks through the exact documentation steps.

What exemptions reduce your assessed value or tax bill?

Exemptions and appeals do different jobs. An appeal argues the assessed value is wrong. An exemption is a legal reduction in taxable value or tax owed that you qualify for whether or not the assessment is accurate.

The homestead exemption is the most common. It cuts taxable value for owner-occupied primary residences, and the dollar amounts vary wildly. Florida's standard homestead exemption removes the first $25,000 of assessed value from all levies plus another $25,000 from non-school levies, for a $50,000 maximum ^[8]. Texas removes $100,000 from the school district portion of taxable value as of 2023 ^[7].

Other common ones: senior exemptions (usually income-tested), disability exemptions, veteran and surviving-spouse exemptions, and agricultural use exemptions. Plenty of homeowners who qualify never apply, because nobody told them the program exists. Your assessed value gets set automatically. Exemptions do not. You file an application, usually once, and renew it in some states.

The National Conference of State Legislatures keeps a regularly updated summary of state property tax relief programs ^[11]. Check it against your state's department of revenue site before you assume you don't qualify for anything.

For how exemptions stack on top of the assessment system in one of the country's most tangled markets, see miami dade property taxes.

How does the appeals process connect back to the assessment?

An appeal is a formal objection to the assessed value, filed with the local board of review, assessment appeals board, or equivalent. The standard is almost always the same: show the assessor's market value estimate is higher than actual market value on the assessment date.

Most jurisdictions offer an informal review first. You call or visit the assessor's office, lay out your comparable sales, and staff can adjust the value with no formal hearing. A good share of appeals end right here. If the informal review fails, you file for a formal board hearing and present evidence there.

What works: recent arm's-length sales of genuinely similar homes, a licensed appraisal, and documented errors on the property record card. What rarely works: what your neighbor told you, a Zestimate, what you paid for the house (purchase price counts only if it falls inside the assessment period and reflects the market), or a general gripe that taxes are too high.

Procedures differ by state on burden of proof (a few states make the assessor prove the value is right; most make you prove it's wrong), hearing format (some are casual, some feel like court), and further appeal rights to state tax courts or circuit courts. Your state department of revenue website has the exact rules. For Midwest homeowners, the hennepin county property tax guide covers Minnesota's procedures in detail.

Can a property tax assessment be appealed more than once?

Yes, in most states. Each new assessment notice opens a fresh appeal window. Missed the deadline this year or lost your case? The next revaluation gives you another swing. You aren't permanently stuck with a prior result, except in a few jurisdictions that hold a settlement or board decision binding for a set number of years.

Some states also allow mid-cycle appeals when something specific happens: a major casualty loss, a change in classification, or a clerical error. California's Assessment Appeals Board system, for one, allows a Proposition 8 decline-in-value claim in any year market value drops below assessed value ^[4].

The practical takeaway is simple. Even if you lost or sat it out last year, pull the new notice the moment it lands and run the comparable analysis again. Markets move. Assessors overcorrect. A home that was fairly assessed eighteen months ago can be overassessed today in a cooling market.

How do commercial property assessments differ?

Commercial properties, including apartment buildings, retail centers, offices, and industrial sites, are usually valued under the income approach. The assessor estimates potential gross income, subtracts a vacancy and expense load, and capitalizes the net income at a market-derived cap rate. The formula: value equals net operating income divided by cap rate.

That gives you two lines of attack in an appeal. You can challenge the inputs (rent assumptions, vacancy rate, expense ratio), or you can challenge the cap rate itself. An assessor using a 5% cap rate in a market where investors are actually paying 6.5% will spit out a badly inflated value. Cap rate evidence comes from published broker surveys, appraisal databases, and real sales of income-producing property.

Commercial appeals also lean harder on formal appraisals, lawyers, and multi-year litigation. The size of the check justifies the expense past a certain property value. Below roughly $2 million in assessed value, a well-documented DIY appeal often lands the same result without paying an attorney's contingency fee.

Our guide to detroit property taxes covers a market with a long commercial reassessment history and a process that is more open to self-represented owners than most people expect. For the broader framework, see our overview of property tax taxation.

What should you do right now if you got your assessment notice?

Record the deadline first. Write it down, put it in your calendar with a two-week buffer, and treat it as sacred. Blowing your appeal rights on a missed deadline is the most avoidable mistake in this whole process.

Next, pull the property record card from your assessor's website and check every field. Square footage, room count, condition grade, outbuildings. Anything wrong might be fixed with a simple correction request before you file anything.

Third, divide your assessed value by the local assessment ratio to get the assessor's implied market value. Look up three to five recent comparable sales. If they run 10% or more below the implied value, you have a case worth chasing.

Fourth, if the numbers hold up, gather your evidence: printed comparable sale sheets with address, sale date, sale price, and specs. A one-page table lining up your property against the comps side by side is often all an informal review needs.

Fifth, call or visit the assessor's office for the informal review first. Bring the documentation. Stay factual, stay calm. Many assessors will drop a clearly inflated value at this stage with no formal hearing at all. If that fails, file the formal appeal before your deadline.

The TaxFightBack appeal kit has ready-to-use worksheets for the comparable analysis and the formal appeal letter, which saves a few hours of formatting. But the real work, finding the data and running the numbers, is something any homeowner with an internet connection can do.

Frequently asked questions

How often are property taxes reassessed?

It depends on the state and county. Some jurisdictions reassess every year using statistical models. Others run a full revaluation every two, four, or even ten years with interim adjustments. The IAAO recommends annual reassessment as best practice, but many counties don't hit that mark. Check your county assessor's website for the official revaluation schedule; it's usually in the FAQ or news section.

What is the difference between assessed value and market value?

Market value is what your property would sell for in an arm's-length deal. Assessed value is market value times the local assessment ratio, which runs anywhere from 10% to 100% depending on state law. Your bill is based on assessed value, not market value directly. Divide your assessed value by the ratio to back into what the assessor thinks your home is worth in market terms.

Can I lower my property taxes without a formal appeal?

Yes, two ways. Check the property record card for factual errors: wrong square footage, a phantom bathroom, a finished basement you don't have. A correction request to the assessor's office fixes those with no hearing. Then make sure you're claiming every exemption you qualify for. Homestead, senior, disability, and veteran exemptions each cut your taxable base, and many eligible owners never apply.

How do I find comparable sales for a property tax appeal?

Your county assessor's website usually has a searchable sales database. Redfin and Zillow both show recent sold prices with property details. The goal is three to five sales that closed within twelve months of your assessment date, within a half-mile to one mile, and similar in size, age, and condition. Sort by sale date, not list price. Document the address, sale price, square footage, and any major differences from your home.

What is a mill rate and how does it affect my tax bill?

One mill equals $1 of tax per $1,000 of assessed value. A 25 mill rate on a $200,000 assessed value produces a $5,000 bill. Local taxing bodies, including school districts, counties, cities, and special districts, each set their own mill rate. Your bill sums all overlapping levies. The assessor sets the value; elected boards set the rates. Appealing your assessment doesn't touch the mill rate.

What happens if I miss the property tax appeal deadline?

In most states you lose the right to appeal that year's assessment entirely. The deadline is typically 30 to 90 days after the assessment notice mails, not after the tax bill arrives. A few states allow late filings under narrow circumstances like demonstrable hardship or clerical error, but those exceptions are rare. Your next shot is usually the following assessment cycle, when a new notice opens a fresh window.

Do I need an appraiser to appeal my property tax assessment?

Not usually, especially for a home. A well-organized set of comparable sales printouts is the standard evidence at most informal reviews and board hearings. A licensed appraisal carries more weight and is worth the cost (roughly $300 to $600 for residential) if the tax savings over several years beat that price, or if the informal review fails and you need stronger evidence for the formal hearing.

Will appealing my property taxes trigger a higher assessment?

This fear is common and almost always wrong. Assessors don't punish owners for appealing. The process is administrative: in nearly all U.S. jurisdictions the board can only lower the value or leave it alone. A handful of states technically let the board raise a value if evidence supports it, but that's extremely rare in practice and usually requires the assessor to actively ask for an increase.

How is property tax calculated in Texas?

Texas appraisal districts assess at 100% of estimated market value as of January 1 each year. For homesteads, state law caps the annual increase in taxable value at 10% over the prior year's appraised value, separate from the market value estimate. The 2023 legislature raised the homestead exemption to $100,000 off the school district levy. Each local taxing unit then applies its own rate to your taxable value to produce the bill ^[7].

What is a homestead exemption and how do I apply?

A homestead exemption reduces the taxable value of your primary residence. Amounts range from a few thousand dollars to $100,000 or more depending on state law. Most require a one-time application filed with the county assessor or appraiser, usually by a spring deadline in the year you want the benefit. You typically need to own and occupy the property as your primary residence on January 1 of the tax year. Check your county assessor's website for the form and deadline.

What is computer-assisted mass appraisal (CAMA) and can it make mistakes?

CAMA is the statistical modeling system most assessors use to value thousands of properties at once without inspecting each one. It ingests sales data, building characteristics, and neighborhood factors to estimate values across whole market areas. Mistakes happen when the input data is wrong (outdated or incorrect property records), when a neighborhood has too few sales for the model to calibrate, or when the model can't tell apart very different micro-locations inside one defined area.

Are lower-income homeowners more likely to be overassessed?

Research from the Lincoln Institute of Land Policy found that in many major U.S. cities, lower-value homes carry higher assessment-to-sale ratios than higher-value homes, meaning owners of cheaper properties effectively pay higher effective tax rates relative to market value ^[1]. This regressivity comes partly from how CAMA models perform at the low end of the value range and partly from lower appeal rates in lower-income communities.

How do I read my property assessment notice?

The notice states your parcel ID, the assessment date, prior assessed value, new assessed value, and the appeal deadline. Some notices show the market value estimate separately from the assessed value. Divide assessed value by the assessment ratio (it should be on the notice or in the instructions) to confirm the implied market value. The filing instructions and address should appear on the notice; if not, call your county assessor's office.

Does buying a house trigger a new assessment?

In most states, no. The assessment follows the annual or cyclical revaluation schedule regardless of a sale. California is the main exception: Proposition 13 resets the assessed base to purchase price at the time of sale, then limits annual increases to 2% ^[4]. A few states have partial reassessment-on-sale rules. If you recently bought below the assessed value, that sale price is strong appeal evidence, as long as it was a genuine arm's-length deal.

Sources

1. Lincoln Institute of Land Policy, Significant Features of the Property Tax: Property taxes generated roughly $630 billion for state and local governments in fiscal year 2021; lower-value homes carry higher assessment ratios in many major U.S. cities
2. International Association of Assessing Officers (IAAO), Standard on Mass Appraisal of Real Property: IAAO sets professional standards for CAMA models including the three approaches to value used by assessors
3. International Association of Assessing Officers (IAAO), Standard on Assessment Appeals: IAAO standard requires median ratio of assessed value to sale price stay within 10% of stated assessment level; recommends annual reassessment; provides state-by-state appeal timeline summary
4. California State Board of Equalization, Proposition 13 Overview: California's Proposition 13 caps annual assessed value increases at 2% and resets base to purchase price at sale; Proposition 8 allows decline-in-value claims when market value drops below assessed value
5. Illinois Department of Revenue, Property Tax System Overview: Illinois assesses most residential property at 33.33% of market value
6. New York City Department of Finance, Property Tax Classes: New York City assesses Class 1 residential property at 6% of market value
7. Texas Comptroller of Public Accounts, Property Tax System Overview: Texas assesses at 100% of market value; homestead cap limits annual taxable value increase to 10%; legislature increased homestead exemption to $100,000 for school district levy in 2023; jurisdictions must publish a no-new-revenue rate annually
8. Florida Department of Revenue, Property Tax Exemptions: Florida's homestead exemption removes first $25,000 of assessed value from all levies and an additional $25,000 from non-school levies; Save Our Homes cap limits annual increase to 3% for homestead properties
9. National Taxpayer Advocate, Property Tax Appeal Rights Overview: Typical appeal deadline runs 30 to 90 days from assessment notice mailing; some jurisdictions allow as few as 20 days
10. National Conference of State Legislatures, Property Tax Assessment: In most states property record cards and assessment data are public record and owners have a legal right to inspect them
11. National Conference of State Legislatures, Property Tax Relief Programs: NCSL maintains a regularly updated summary of state property tax relief programs including exemptions for seniors, disabled owners, and veterans