Property tax calculator

What the number means

Property tax is a local tax: counties, cities, school districts and special districts each add their own levy, and the sum is applied to the taxable value of your property. It is the main reason two houses of equal price can have bills thousands of dollars apart. The calculator takes your inputs and shows each step, so you can see where an exemption, a low assessment ratio or a state multiplier changes the result.

Three worked cases show the mechanics. With the default numbers, a $300,000 home at a 35% ratio has $105,000 of taxable value and, at 60 mills, a tax of $6,300. The Cook County Assessor’s own sample, $100,000 of market value, a 2.6685 multiplier, a $7,000 exemption and a 10% rate, comes to $1,968.50. In California, where Proposition 13 sets the base rate at 1% of taxable value, a home assessed at $800,000 with an extra 0.12% for voter-approved bonds (the 0.12% is illustrative) owes $8,960.

How is property tax calculated?

Every county runs the same three steps, though the numbers differ. First the assessor sets a value for the property. Second, a fraction of that value, called the assessment ratio, becomes the assessed value, and any exemption (homestead, senior, veteran) is subtracted from it. Third, the combined tax rate of all your local districts is applied to what is left. In a formula: tax = (market value × assessment ratio × any state multiplier − exemptions) × tax rate + flat charges. On the default numbers, a $300,000 home assessed at 35% has an assessed value of $105,000; at 60 mills the tax is $6,300 a year, or $525 a month, which is 2.1% of the market value. The 60 mills is a teaching number, not the rate of any real county.

What is a mill, and how do I convert mills to a percentage?

A mill is one thousandth of a dollar: 1 mill is $1 of tax for every $1,000 of taxable value, or 0.1%. So 12 mills, $1.20 per $100 and 1.2% all mean the same thing: on a $200,000 taxable value each gives $2,400, $2,400 and $2,400. To change mills to a percentage, divide by 10; to change a percentage to mills, multiply by 10. The calculator accepts any of the three units, because county tax offices print them differently. Remember that the rate applies to the taxable (assessed) value, not to the market value, unless your county assesses at 100%.

Why is the assessment ratio not 100% in some places?

Some states and counties tax only a share of market value. Ohio law caps the taxable value of real property at 35% of its true value (Ohio Revised Code section 5715.01(B)), and the Cook County Assessor in Illinois uses 10% of market value for single-family homes and condos. California assesses at market value when a property is bought or built, but limits the rate: Proposition 13 caps the property tax at 1% of taxable value plus the rate needed for voter-approved bonded debt, and generally limits the yearly increase of the base year value to 2% until a change in ownership or new construction resets it (State Board of Equalization, Publication 29). A low ratio is not a tax break by itself: counties with a 10% or 35% ratio set higher nominal rates to raise the same money. Compare the effective rate (tax divided by market value), which this calculator shows under the answer.

What is the equalizer or multiplier?

Illinois adds one more step. After the Cook County Assessor sets the assessed value at 10% of market value, the state applies a yearly equalization factor so that all counties are on the same footing, giving the equalized assessed value (EAV). Exemptions come off the EAV, and the local rate is applied to the rest. The assessor's own sample uses a multiplier of 2.6685 and a $7,000 exemption on a $100,000 home with a 10% rate: $10,000 assessed, $26,685.00 equalized, $19,685.00 after the exemption and $1,968.50 in tax. Leave the multiplier at 1 if your state has no such step. The factor changes every year, so take it from your county or state revenue department rather than from an old bill.

How do I use the monthly figure for escrow?

Lenders who collect property tax with the mortgage payment divide the expected annual bill by 12 and hold the money in an escrow account. The monthly figure here is that division: the annual tax $6,300 on the default numbers is $525 a month. Your servicer re-checks the account every year, and if the bill rises you get a shortage notice and a higher payment. Because many counties reassess after a sale, the bill on a house you are about to buy may be higher than the seller's. Run the numbers with your own purchase price and the county's reassessment rule; then add the result to the monthly payment in the mortgage calculator.

What exemptions can I enter?

Enter the amount of assessed value that your exemptions remove, in dollars: a homestead exemption, a senior or veteran exemption, for example. The calculator subtracts it from the assessed (equalized) value and never lets the taxable value go below zero. Exemptions are set by each state or county and differ in kind: some remove a fixed dollar amount of value (the Cook County sample above removes $7,000 of EAV), others cap how fast the assessed value may grow, others give a credit against the bill. This tool handles only the first kind. If your exemption is a credit against the bill, subtract it from the answer yourself.

What does this calculator leave out?

Rate changes after a levy vote, caps on yearly increases other than a simple exemption, phased-in assessments, special assessments for streets or sewers (you can add them as flat charges), delinquency penalties, state rebate programs and the federal deduction. The federal deduction for state and local taxes, including property tax, is limited by a cap (see the standard vs itemized deduction calculator on this site); most households take the standard deduction, so property tax often brings no federal tax saving at all.

Common mistakes

Using the market value where the rate expects the assessed value is the commonest slip: a 60-mill rate applied to $300,000 gives $18,000, not $6,300. Second, using only one district’s rate: your bill is the sum of the county, city, school and special-district levies. Third, treating the bill as fixed: levies are voted on, and values are reassessed on a county schedule or after a sale. Fourth, comparing states by nominal rate alone; the effective rate, tax divided by market value, is the fair comparison.

An estimate for planning only — not tax advice; your tax bill decides. Sources: Cook County Assessor, “How are my taxes calculated?” (10% level of assessment, state equalizer, exemptions removed before the rate; checked October 27, 2026); Ohio Revised Code section 5715.01 (taxable value capped at 35% of true value); California State Board of Equalization, Publication 29, California Property Tax: An Overview (Proposition 13: 1% rate plus voted bonded debt, 2% annual limit on the base year value). Find your county’s own ratio and rate on its assessor or treasurer site. Next steps: add the escrow to the mortgage calculator, check what you can afford in the home affordability calculator, see the federal side in the standard vs itemized deduction calculator and the sales tax side in the sales tax calculator. How we check our calculators.