The records behind the numbers
The headline figure is an estimate. It matches home sales from the last two years (October 2024 to September 2026) to Oakland County’s current parcel records: assessed value, taxable value and where the tax bill is sent. Tax is figured at the 2025 Michigan Treasury millage rates for each home’s community. Sale prices are used only in aggregate; no individual sale from that data set is published on this site.
The case studies and the free check’s sale comparisons come from a different, fully public source: each community’s own published residential sales or economic condition factor study.
The free check reads the county’s parcel records for any home in Oakland County and applies the 2025 rate for that home’s community and school district. Sale comparisons come from each community’s own published residential sales or economic condition factor study, for about 40 of the county’s communities, covering roughly four in five homes. Where a community has not posted its study, the check uses the owner’s own figure instead.
How the estimate is built
Of the 17,692 Oakland County homes bought between October 2024 and December 2025, 1,289 screen as both over-assessed and uncapped: the city’s value is more than 10 percent above the sale price, and the cap has already come off, so the difference reaches the tax bill. Sale prices are carried forward to the December 31, 2025 valuation date at 2.2 percent a year, the market trend visible in the communities’ own sales studies, and gaps too large to be anything but a rebuild are left out. Across those 1,289 homes:
Estimated total overpayment
About $2 million / yr
Median
$1,126
Middle halfTwenty-fifth to seventy-fifth percentile
$751 – $1,781
Share of recent buyersBought October 2024 to December 2025
About 1 in 14
The figures describe that group, not every recent buyer. Most recent buyers have no case at all: 81 percent are assessed in line with what they paid, and another 11.5 percent are still protected by the cap. Homes bought in 2026 are not counted yet; their bills still use the seller’s capped value until the cap lifts in 2027.
Checked against the communities’ own studies
The same screen run on the sales in about 40 communities’ own published studies, which cover mostly 2023 to early 2025, finds $1.0 to $1.6 million a year across those communities, depending on whether sale prices are adjusted for the market. Every home counted there was traced to its line in the study, and a home counts only where the community’s own printed assessment agrees. The two sources find recent buyers over-assessed at close to the same rate; the headline covers more buyers and the whole county.
What the figures are not
Every “tax on the gap” figure on this site is the tax on the difference between the city’s value and a recorded sale price. It is not a predicted refund and it is not a promised reduction.
“The purchase price paid in a transfer of property is not the presumptive true cash value of the property transferred.”
MCL 211.27(6)Because of that provision, a gap between an assessment and a sale price is a reason to look rather than a result. An appeal succeeds on the city’s own valuation method applied correctly to the property, which is a separate piece of work from the screen these figures come from.
Known limitations
- Homestead status is inferred. We infer it from whether the tax mailing address matches the property address. That is a good proxy and it is not a certainty, so per-home figures are estimates.
- Millage rates are prior-year. Figures use 2025 Michigan Treasury rates. Rates move a little each year and a current bill may differ slightly.
- Sale prices are as recorded. A recorded price may include or exclude concessions, and we cannot see the terms of a transaction from the record alone.
- The screen is not the analysis. These figures identify properties worth examining. They do not establish that any particular assessment is wrong.
Public sources used
- City of Farmington Hills residential sales studies, economic condition factor studies, the ECF area map, the land value atlas and the land ratio studies.
- City of Farmington 2026 sales study and supporting valuation studies.
- Oakland County open parcel data, covering roughly 490,000 parcels across 62 communities.
- Michigan Department of Treasury millage rate tables, including the 2025 Total Rates report for every Oakland County community and school district, and State Tax Commission forms and bulletins.
- Residential sales and economic condition factor studies posted by Oakland County communities and by Oakland County Equalization for the communities it assesses, 2026 roll.
- Oakland County school district boundaries, used to apply the right school district’s rate to each home in the free check.
- The Michigan General Property Tax Act, Public Act 206 of 1893, as amended.
If you want to check any figure on this site against its source, write to us and we will tell you exactly where it comes from.