What Is a Mill
A mill is one-tenth of one cent, or $0.001. It represents $1 in property tax for every $1,000 of assessed property value. If your property is assessed at $300,000 and the millage rate is 50 mills, your annual property tax is $15,000 (50 × $300,000 ÷ 1,000).
The mill measurement standardizes tax rates across jurisdictions with different assessment bases. A 50-mill rate in one county is directly comparable to a 50-mill rate in another, making it easier to understand tax burden variation by location.
Mills and Your Assessment Appeal
Mills matter in property tax appeals because they clarify where your tax burden originates. Your total tax bill splits into two components: the assessed value and the millage rate applied to it. If your assessment is too high, the mill rate is irrelevant to that specific problem. If the mill rate is excessive, that's a separate issue handled at the municipal level through budgeting and tax levy votes.
During a board of review hearing, focus on the assessed value using comparable sales and appraisal methods. Mills determine how much that assessment translates to dollars owed, but they don't determine whether the assessment itself is accurate.
Understanding Mills Relative to Assessment Ratios
Assessment ratios and mills work together. Many states require assessors to maintain a uniform assessment ratio (often 50%, meaning properties are assessed at 50% of market value). If your assessed value exceeds this ratio compared to recent comparable sales, you have grounds for appeal regardless of the millage rate applied.
For example, if comparable sales show your home should be worth $400,000, but you're assessed at $350,000 in a 50% ratio state, you're assessed at 87.5% of value. That overassessment exists independent of whether mills are 40 or 60.
Typical Mill Rates by Property Type
- Residential property: 30 to 70 mills across most U.S. jurisdictions
- Commercial property: 40 to 80 mills (higher in urban areas)
- Agricultural property: 10 to 40 mills (varies by state exemption policies)
States like Michigan, Ohio, and Wisconsin publish mill rate data annually. Your county assessor's office provides the specific rate for your property.
Common Questions
- If I lower my assessed value in an appeal, do I get a refund on overpaid taxes? Many jurisdictions offer refunds for the current tax year and sometimes prior years if the assessment change is approved before the tax bill is finalized. File your appeal before the applicable deadline to be eligible. Some states allow three to five years of back claims.
- Can I appeal the mill rate itself? No. Mill rates are set through municipal budget processes and voter approval, not the assessment process. Your appeal challenges the assessed value, not the rate applied to it. Contact your township or city council if you believe the millage rate is unjust.
- How do mills affect commercial property appeals differently? Commercial properties often face higher mill rates and are appraised using income capitalization or cost approach methods rather than comparable sales. Mills function the same way mathematically, but the appraisal methods differ significantly.