How Iowa property tax actually works: the rollback step

Property-tax math in Iowa has a trap built into it: assessed value is not taxable value. Anyone who multiplies a property’s assessment by the published levy without applying the state rollback first will produce a number that looks precise and can be badly wrong.

For assessment year 2025, the Polk County Assessor publishes a residential rollback of 0.445345 and a commercial rollback of 0.900000.1 In plain language, 44.5345% of a residential assessment and 90% of a commercial assessment are taxable before credits, exemptions, or other adjustments.

The formula

Taxable value = assessed value × rollback

Annual property tax = taxable value × (consolidated levy ÷ 1,000)

The 2024 consolidated levy for the dominant Des Moines City / Des Moines Schools district is 42.32446 per $1,000 of taxable value.2

Consider a property assessed at $1 million:

Multiplying $1 million directly by 42.32446 mills would produce $42,324 — more than double the residential result.

Why this site shows two answers

Most properties in this database are hospitals, schools, churches, offices, care facilities, or institutional land. If an exemption ended, many would likely be classified as commercial or multi-residential rather than residential. That makes the commercial rollback a plausible comparison.

But homeowners encounter property tax through the residential rollback. Asking “what if exempt properties paid what homeowners pay?” is also a legitimate civic question. That makes the residential comparison meaningful.

Neither scenario is a prediction. Neither is a bill. Choosing only one would hide the most consequential assumption in the calculation. We therefore show both with equal prominence:

These totals use the net exempt value of each parcel. For the 31 partially exempt parcels, value already on the tax roll is removed before the comparison.3

The levy is not all City revenue

The consolidated levy funds multiple public bodies, not only the City of Des Moines. The City says about 33% of a resident’s property-tax bill goes to city government, while the balance funds Des Moines Public Schools, Polk County, Broadlawns Medical Center, DART, DMACC, and the State.4

That means a citywide $47.7 million or $96.3 million scenario is not the amount the City government would receive. At the City’s own approximate 33% share, the rough city portion would be $15.7 million or $31.8 million respectively. Those secondary figures are estimates because the actual share varies with the levy district and tax year.

Des Moines has more than one levy

The city spans multiple school districts and special districts. The Assessor’s 2024 table shows 23 combinations, ranging from roughly 39.93 to 45.65 per $1,000.2 The site uses 42.32446 as a disclosed default because it is the Des Moines City / Des Moines Schools district, not because it is universal.

Use the tax-gap calculator [blocked] to change the assessed value and levy yourself. The formula is the product.

References

1. Polk County Assessor — Iowa rollback rates
2. Polk County Assessor — Des Moines jurisdiction regular levies
3. Polk County Assessor — Commercial Inventory for Polk County
4. City of Des Moines — Research and Budget

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Editorial disclosure

This article was researched and drafted with AI assistance, then checked against the cited public records. The data transformations and arithmetic are documented on our Methodology [blocked] page. AI does not decide whether a property qualifies for an exemption; that authority belongs to the Polk County Assessor and Iowa tax authorities.