What Is Assessment Ratio?

The percentage of a property's market value that a state uses to calculate the assessed value for property tax purposes.

Detailed Explanation

The assessment ratio is the bridge between what your home is worth on the open market and the number the county actually uses to calculate your tax bill. Every state sets its own ratio, and the range is enormous. In states that assess at 100% of market value (like Texas, California, and Florida), your assessed value should theoretically equal what your home would sell for. But in states with lower ratios, the assessed value is a fraction of the market price. For example, South Carolina assesses owner-occupied homes at just 4% of market value, so a $300,000 home would have an assessed value of $12,000. The millage rate is then applied to that $12,000 figure, not the full $300,000. Understanding your state's ratio is critical because it determines whether your assessment is actually too high. If your state assesses at 25% and your home is worth $400,000, your assessed value should be around $100,000. If the county has you at $120,000, you're overassessed by $20,000 in assessed value, which translates to a $80,000 overestimate of your market value. Not every "percentage of value" figure you see is a straight assessment ratio, though. Nevada assesses at 35%, but of "taxable value," a replacement-cost-minus-depreciation figure the state calculates independently, not 35% of market value directly. The distinction matters if you are trying to reverse-engineer whether your assessment is too high: dividing your assessed value by the stated ratio only gets you back to market value in states where the ratio is applied directly to market value in the first place.

How It Varies by State

South Carolina4%

Lowest in the nation for owner-occupied homes. Investment properties assessed at 6%.

Tennessee25%

Residential property assessed at 25% of appraised value. Commercial at 40%.

Georgia40%

All property assessed at 40% of fair market value statewide.

Ohio35%

County auditors assess at 35% of market value. Reassessment every 6 years.

Texas100%

Assessed at full market value. No state income tax, so property taxes are higher.

Alaska100%

Full market value. Many boroughs offer generous senior exemptions.

Nevada35% of taxable value

Not a straight percentage of market value: taxable value is a separate replacement-cost-minus-depreciation calculation, and assessed value is 35% of that figure, per NRS 361.225.

Illinois33.33% statewide, 10% in Cook County

The 33.33% figure is the statewide standard, but Cook County uses its own classification system with a 10% initial assessment level for residential property, then applies a state equalization factor (about 3.04 for 2024) to bring its equalized assessed value back in line with the statewide standard. The initial assessment level and the final effective ratio are different numbers, and both get called "the assessment ratio" depending on the source.

Common Misconceptions

Myth:A lower assessment ratio means lower taxes

Reality:States with low ratios often compensate with higher millage rates. South Carolina's 4% ratio comes with some of the highest mill rates in the country.

Myth:The assessment ratio is the same for all property types

Reality:Most states apply different ratios to residential, commercial, and agricultural property. In Tennessee, homes are assessed at 25% while commercial property is assessed at 40%.

Myth:If my state assesses at 100%, my assessment should match my Zillow estimate

Reality:Zillow estimates are not official appraisals. Counties use their own mass appraisal methods, which may diverge significantly from online estimates. The county's assessment date also matters.

Myth:Every stated percentage is a ratio applied directly to market value

Reality:Not always. Nevada's 35% applies to a separately calculated "taxable value" (replacement cost minus depreciation), not straight market value, so you cannot always back into market value just by dividing assessed value by the stated ratio.

Myth:Cook County, Illinois assesses residential property at 33.33% like the rest of the state

Reality:Cook County actually starts residential property at a 10% assessment level, well below the statewide 33.33% standard. A state equalization factor is then applied on top to bring Cook County's final equalized assessed value roughly back in line with the rest of Illinois, so the 10% and 33.33% figures both describe the same county at different stages of the calculation.

Impact on Your Tax Bill

In Ohio (35% ratio), if your home is worth $250,000, your assessed value should be $87,500. If the county has you at $100,000 assessed ($285,714 implied market value), you're overpaying. At Ohio's average effective rate of 1.59%, that $12,500 overassessment costs you about $199 per year in excess taxes.

Frequently Asked Questions

How do I find my state's assessment ratio?

Your county assessor's website or your state department of revenue publishes the current ratio. It is also frequently printed directly on your assessment notice or tax bill.

Does a low assessment ratio mean I pay less in property tax overall?

Not necessarily. States with low assessment ratios, like South Carolina at 4%, typically offset it with much higher millage rates, so the effective tax rate on your home's actual value can still be comparable to, or higher than, a 100%-ratio state.

Can I calculate my home's implied market value by dividing assessed value by the ratio?

In most states, yes, that math works because the ratio is applied directly to market value. It does not work in states like Nevada, where the ratio applies to a separately calculated taxable value rather than market value directly.

Is the assessment ratio the same for every type of property?

Often not. Many states apply different ratios to residential, commercial, and agricultural property. Always confirm the ratio for your specific property class, not just a general statewide figure.

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