Property tax appeals usually start with one question: is the county’s value too high? We reviewed 2025 property records in Clayton County and Gwinnett County and compared each county’s appraised value against an estimated fair market value, or FMV.
A property was counted as overappraised when its 2025 county appraised value was greater than estimated fair market value, or FMV.
The main finding
Clayton had the higher overappraisal rate. Gwinnett had the larger dollar impact.
Across both counties, more than 155,000 matched properties were appraised above estimated FMV.
| County | Above FMV | Impact |
|---|---|---|
| Clayton | 38,065 52.7% |
$1.43B median gap $20,900 |
| Gwinnett | 117,262 47.6% |
$6.33B median gap $24,000 |
What that means by county
In Clayton County, 38,065 of 72,250 matched properties were appraised above estimated FMV. That is 52.7% of matched properties.
The median Clayton county value and median FMV estimate were both $227,400, which sounds balanced at first. But property by property, more than half of the matched properties were above FMV. Among those overappraised properties, the median gap was $20,900.
In Clayton County, the typical overappraised property was valued about $20,900 above estimated FMV.
In Gwinnett County, 117,262 of 246,450 matched properties were above estimated FMV. The rate was lower than Clayton’s, at 47.6%, but the dollar impact was much larger: about $6.33 billion in appraised value above FMV.
The gap was not minor
Some properties were only slightly above FMV. But many were not. Clayton was more severe at every percentage threshold.
| Threshold | Clayton | Gwinnett |
|---|---|---|
| Any amount above FMV | 52.7% | 47.6% |
| More than 5% above FMV | 37.8% | 25.6% |
| More than 10% above FMV | 24.7% | 11.3% |
| More than 20% above FMV | 9.2% | 2.0% |
Attached housing stood out
One of the clearest patterns was property type. Condos and townhomes were much more likely to be appraised above FMV than single-family homes.
Overappraisal by property type
Attached housing showed some of the highest overappraisal rates in both counties.
Takeaway: Attached housing owners may be more likely to have county values above estimated FMV.
The hotspots were local
The overappraisal issue was not spread evenly. In Clayton, College Park was the clearest city-level hotspot. Clayton ZIP 30349 also stood out. In Gwinnett, the strongest local hotspots included ZIP 30071, Auburn, Grayson, and Loganville.
| Area | County | Above FMV |
|---|---|---|
| College Park | Clayton | 77.6% |
| ZIP 30349 | Clayton | 68.5% |
| ZIP 30071 | Gwinnett | 60.8% |
| Auburn | Gwinnett | 56.6% |
| Grayson | Gwinnett | 54.3% |
| Loganville | Gwinnett | 53.0% |
Newer homes were another warning sign
Year built showed a useful pattern without needing another table. In Gwinnett, homes built from 2010 to 2019 had a 69.9% overappraisal rate. Homes built from 2000 to 2009 had a 62.1% rate.
Clayton showed a similar but less extreme version of this. Homes built from 1990 through 2019 were more likely to be above FMV than older homes.
Clayton also had a useful recent-sale check. For 2025 transfers, the FMV estimate was closer to the recorded sale price 79.7% of the time, with a median FMV error of $2,300 compared with a median county appraisal error of $41,150.
The takeaway for homeowners
A high property tax bill usually starts with a high property value.
In Clayton, more than half of matched properties were appraised above estimated FMV. In Gwinnett, slightly under half were above FMV, but the total value above FMV was much larger.
The strongest warning signs were attached housing, certain ZIP codes and local markets, newer homes, and large gaps between county value and estimated FMV.
If your county value looks high, compare it against recent nearby sales, similar homes, and your property’s actual condition.
The appeal starts with the value — and the deadline usually comes before the bill.