Assessed Value vs. Market Value: Why Your Home's Tax Bill Doesn't Match the Price You'd Pay

You're scrolling through Zillow and see your home is worth $450,000—yet your property tax bill is based on an assessed value of just $310,000. According to Experian, assessed values are often calculated at 50% of market value or less, depending on your state's assessment ratio. The gap between what your home could sell for and what the tax assessor says it's worth can cost you thousands in confusion and unexpected tax hikes. Understanding the difference between assessed value and market value isn't just about curiosity—it's the key to budgeting for taxes, appealing unfair assessments, and making smart real estate decisions.

Assessed Value vs. Market Value: The Core Difference

Assessed value is what your local tax assessor determines your property is worth for tax purposes. Market value is what your home would likely sell for in today's real estate market. These two numbers are rarely the same, and the gap matters because assessed value directly determines your property tax bill.

Here's the formula: Assessed Value × Tax Rate = Property Tax Bill. Market value, by contrast, is determined by recent comparable sales, location demand, condition, and market trends. A home in a hot neighborhood might have a market value of $500,000 while its assessed value sits at $350,000 because the tax assessor uses a formula or percentage rather than actual sale prices.

The ratio between assessed and market value varies dramatically by state. In California, assessed value is capped at 1% of the purchase price (thanks to Proposition 13, passed in 1978), while across the US the average assessment ratio ranges from 80% to 100% depending on the state and county. New York City uses tax-class-based ratios where different property types are assessed at different percentages of market value—meaning a condo owner and a townhouse owner on the same block might have completely different assessment ratios, even if their homes have similar market values.

Scenario	Assessed Value	Market Value	Likely Result
Hot market, limited inventory	Often lags behind	Rises quickly	Home sells above assessed value and taxes may catch up later
Slow market, recent assessment	May stay high from prior cycle	Falls	Owner may have grounds to appeal if assessment exceeds comparable sales
Renovated home in stable neighborhood	May rise gradually after reassessment	Can jump immediately	Sale price reflects upgrades sooner than the tax bill

Assessed value changes on a schedule—typically every 1 to 5 years depending on your county's reassessment cycle. Market value changes constantly based on actual buyer demand. This timing mismatch is why you can see your neighbor's identical house sell for $480,000 while your tax bill is still based on a $320,000 assessed value from 3 years ago.

Practical Application: How to Find Your Assessed Value and Calculate Your Real Tax Bill

Finding your assessed value takes 10 minutes and one online search. Most counties publish assessor's parcel records online for free. Search your county assessor's website (usually "[your county] assessor online search") and enter your address or parcel number. You'll see the assessed value, land value, improvement value, and sometimes the date of the last assessment.

Once you have that number, calculating your actual property tax is straightforward: multiply your assessed value by your local tax rate (often called the "mill rate" or expressed as a percentage). For example, if your assessed value is $300,000 and your tax rate is 1.2%, your annual property tax is $3,600. That's $300 per month—a number you can plug directly into a mortgage payment estimate.

Use our free Mortgage Calculator to estimate your full monthly payment, including taxes, insurance, and HOA fees if applicable. This matters because many homebuyers focus only on the mortgage rate and forget that property taxes can swing your total monthly cost by $200 to $400 or more.

If you live in California or another state with strict assessment caps like Proposition 13, your assessed value grows slowly even if the market skyrockets. California's rule limits annual assessment increases to 2% per year, meaning a home purchased for $400,000 in 2000 might still carry an assessed value under $800,000 today, even though comparable homes sell for $1.2 million. That homeowner gets a massive tax advantage compared to a new buyer next door—and understanding this gap helps you decide whether it's worth challenging an assessment or refinancing into a new purchase scenario.

Real-World Examples: How Assessment Gaps Play Out in Hot and Slow Markets

In Austin, Texas, one homeowner purchased a condo for $285,000 in 2022 when the market was cooling. The assessed value came in at $280,000. By 2025, the neighborhood boomed and comparable condos sold for $385,000—a $100,000 jump in market value. But the assessed value only rose to $310,000 because the county's reassessment cycle is every 2 years and the last full revaluation happened early 2023. This homeowner's taxes are still based on $310,000 while she could sell for $385,000. The lag worked in her favor until 2026, when the next reassessment will likely push her assessed value closer to $380,000, causing a sudden tax spike.

In New York City, the situation is more complex because of tax-class rules. According to the NYC Department of Finance, assessed value is based on a percentage of market value that depends on the tax class. For a condo in Tax Class 1 (residential), the assessed value can grow no more than 6% per year and no more than 20% over a 5-year period. A condo owner with an assessed value of $500,000 might see the market value jump to $650,000 after a renovation, but the assessed value is capped at growing only $30,000 per year. The owner's taxes lag behind the true market value by design, which protects long-term owners but means new buyers pay full market price while older owners carry lighter tax loads.

Try our free California Mortgage Calculator if you're considering a purchase in a Proposition 13 state—it shows you exactly how the 2% annual cap on assessed-value increases affects your long-term tax burden compared to a buyer in a state with annual full reassessments.

South Dakota provides another contrast: assessed value is set at 50% of market value across the board, according to Experian. This 50% ratio is straightforward and predictable—if your home's market value is $400,000, the assessed value will be exactly $200,000. Buyers in South Dakota know the math in advance, which simplifies budgeting.

Why Your Taxes Went Up Even When the Market Slowed Down

This is the #1 frustration homeowners express: "My taxes went up even though the market slowed down—how can assessed value still increase?" The answer lies in assessment cycles and caps.

Most counties reassess properties on a 1- to 5-year schedule. If your home was last assessed during a hot market in 2023 and the reassessment happens in 2025, you're now paying taxes on a value locked in from a peak year. Meanwhile, the actual market has cooled, but the assessor's books haven't caught up. You have grounds to appeal.

Additionally, if you made improvements—a new roof, kitchen remodel, or addition—the assessor will bump up the assessed value immediately in most states. That's separate from the general reassessment and happens on the assessor's schedule, not the market's.

Proposition 13 owners in California get relief: once assessed, values can only rise 2% per year regardless of market swings. If the market crashes 30%, your assessed value still rises 2%. This sounds unfair when the market is down, but it protects you in both directions—your taxes won't spike if the market rips upward.

How to Challenge an Assessment If You Think It's Too High

If your assessed value seems out of line with recent comparable sales, you can appeal. Start by comparing your assessed value to 3–5 homes in your neighborhood that sold in the last 12 months. If the comps support a lower value, you have a case.

Most counties accept formal appeals during a specific window each year—usually 30 days after the assessment notice arrives. You'll file a form (available on the assessor's website) and present your evidence: recent sales of similar homes, professional appraisals, or photos showing your home's condition is worse than the assessor assumed.

Success rates vary. In slow markets with recent assessments that assumed high prices, appeals often win. In hot markets, appeals rarely succeed because the assessor's assumptions were accurate. Use our Affordability Calculator to explore what your home is realistically worth in today's market—that data becomes evidence in an appeal.

Frequently Asked Questions

What is the difference between assessed value and market value?
Assessed value is the property value used by tax assessors to calculate your tax bill; it's often a fixed percentage of market value set by state law or reassessed on a cycle. Market value is what your home would sell for today based on recent comparable sales and buyer demand. Assessed value is controlled by the government and doesn't change every year; market value changes constantly with the real estate market. Many homeowners have assessed values significantly lower than market value, which is why your tax bill doesn't match what Zillow says your home is worth.

Why is assessed value usually lower than market value?
States intentionally set assessed values lower than market values to prevent extreme tax spikes. Assessment ratios vary by state—South Dakota uses 50%, California uses 1% of purchase price, and most states use 80–100% of market value—but nearly all keep assessed value below the true selling price. Additionally, assessed values are updated on a cycle (every 1–5 years), so they lag behind fast-moving markets. When the real estate market heats up, market values jump immediately while assessed values catch up slowly, creating a gap that protects homeowners from sudden tax increases during booms.

How do tax assessors calculate assessed value?
Tax assessors use three main methods: the sales comparison approach (looking at recent comparable sales), the income approach (for rental properties), and the cost approach (estimating replacement cost minus depreciation). Most residential properties are assessed using comparables—the assessor identifies 3–10 homes similar to yours that sold recently and adjusts for differences in size, condition, and location. The result is multiplied by the state's assessment ratio (e.g., 50% in South Dakota) to get the final assessed value. Assessors update values on a reassessment cycle; some do it annually, others every 3–5 years, which is why your assessed value can feel outdated.

Can assessed value be higher than market value?
Yes, though rarely. In a down market, if your home was assessed at the peak 3 years ago and the market has fallen 20%, your assessed value could exceed comparable sales. This gives you grounds for an appeal—you can argue that recent comps support a lower value. Conversely, in California and other Prop 13 states, assessed values can stay artificially low because they're capped at 2% annual increases, so assessed value is almost never higher than market value. In states without caps, if reassessment is delayed and the market drops sharply, you could have an assessment that's temporarily too high.

How do I appeal my property tax assessment?
File a formal appeal with your county assessor during the appeal window (usually 30 days after receiving the assessment notice). Most counties accept appeals online or by mail using a standard form. Submit evidence: photographs showing your home's condition, a professional appraisal, recent comparable sales in your neighborhood, or documented defects (foundation issues, outdated systems). If the assessor agrees, your assessed value is lowered and your taxes drop retroactively. If you disagree with the assessor's response, most states allow a second appeal to an assessment review board or the county board of supervisors. Success rates are highest in down markets and when your comps clearly support a lower value.

Try our free Mortgage Calculator to run your own numbers in seconds.

The Bottom Line

The gap between assessed value and market value is real, and it affects your tax bill, your monthly budget, and your appeal options. Know your assessed value, compare it to recent comps, and don't be afraid to appeal if it's out of line—thousands of homeowners win appeals every year by simply presenting evidence. Use our Mortgage Calculator to model the full cost of ownership, including property taxes based on your actual assessed value, so you make decisions with complete financial clarity.