How Wisconsin Property Tax Is Set

Every December, Wisconsin homeowners open a property tax bill, and many assume the number reflects a tax rate someone in Madison picked. It doesn’t. A property tax bill is built backward from local budgets, and once you see how, a lot of common worries (like “my assessment went up, so my taxes will too”) turn out to be only partly true.

The levy comes first

Each year, every body with taxing power over your property, your city, village, or town; your county; your school district; your technical college; and the state’s small forestation tax, adopts a budget. It totals its expected spending, subtracts what it expects from state aid, shared revenue, fees, and other sources, and whatever is left must be raised from property tax. That amount is the levy ¹.

In other words, the total property tax collected is set by budgets, not by property values. Your municipality’s treasurer then collects the tax for all the bodies at once: municipality, school, county, and state ¹.

Assessment divides it up

The local assessor places a value on every taxable property, and that assessed value decides what share of the levy your property carries. By law, assessments of non-farm property are based on market value as of January 1. The state recognizes that no municipality can reassess everyone at market value every year, so it requires each municipality’s assessments to be within 10 percent of market value at least once every five years ¹. (Farmland is the big exception: it’s assessed on its value for farming, not its market value, which the constitution allows ¹.)

Because towns assess at different percentages of market value, the Department of Revenue also computes an equalized value for every municipality, an estimate of its full market value. Equalized values, not local assessments, are used to split county, school, and technical college levies among the municipalities that share them, so a town that assesses low doesn’t dodge its share ¹.

From levy to rate

The tax rate is just the levy divided by the total assessed value, usually stated in dollars per $1,000 of value, the mill rate ¹. The Department of Revenue’s own example uses the imaginary city of Badgerville ¹:

• The city levies $200,000, the county $230,000, the school district $560,000, and the state forestation tax $10,000: $1,000,000 in all.
• Badgerville’s total assessed value is $25,000,000.
• Rate: $1,000,000 ÷ $25,000,000 = 0.04, or $40 per $1,000.
• A home worth $50,000, assessed at 90 percent of market value, is assessed at $45,000. Its tax: $45,000 × 0.04 = $1,800, less a $300 state credit, for $1,500 due.

Now the key point. If the town revalues and every assessment doubles while the levy stays the same, the rate is cut in half ¹. Your bill changes only if your property’s value rose faster or slower than everyone else’s. A higher assessment shifts more of the levy to you only relative to your neighbors; what raises everyone’s taxes is a higher levy.

Limits on the levy

The state caps how fast local levies can grow. A municipality may generally increase its levy over the previous year only by the percentage growth in its equalized value from net new construction, new buildings minus demolitions. With no new construction, the allowable increase is zero ^{2 3}. There are exceptions, such as certain debt payments, and voters can approve going over the limit in a referendum ².

If you think your assessment is wrong

The appeal process starts each spring or summer when the assessment roll is finished. First comes Open Book, a period when you can review your assessment and talk with the assessor informally; the assessor can still fix errors then. After it closes, any change requires a formal appeal to the Board of Review, which begins at least seven days after Open Book. You must file a written objection form, and you’ll need evidence of your property’s market value as of January 1, such as recent sales of comparable homes ¹.

Remember what you’re appealing: your value, not your tax. Arguing that taxes are too high belongs at budget hearings, where the levy is actually set.

Try it

Find your most recent property tax bill. Look for the assessed value, the “average assessment ratio,” and the estimated fair market value; the bill shows how much went to each taxing body this year and last. Divide each body’s tax by your assessed value to see its share of the rate. Which body takes the largest share?