Buyers frequently budget from the property tax figure shown on a listing and then receive a much larger bill. The sale itself is what changed the number.
Assessed value is not market value
Property tax is calculated from an assessed value maintained by a county or municipal assessor, and that figure is a record rather than a live market price.
Assessments are updated on a cycle, and in many jurisdictions annual increases to an existing owner's assessed value are limited by statute or by state constitutional provisions.
A home held for a long time can therefore carry an assessed value well below what it would sell for, with the gap widening every year the owner stays.
A sale resets the record
A transfer of ownership is the event that lets the assessor reset the assessed value, typically toward the price the property just demonstrated it could command.
The prior owner's protections do not transfer with the deed. The new owner starts from the reset figure and begins accumulating limits from there.
That is why the listed tax amount describes the seller's situation, not the buyer's, and why it can understate the buyer's bill substantially in a long-held home.
The rate is set separately from the value
The bill is the assessed value multiplied by a rate assembled from overlapping taxing authorities, including counties, cities, school districts and special districts.
Those bodies set rates through their own budget processes, so a rate can change independently of any change in the home's value.
A homeowner can therefore see a higher bill in a flat market, or a stable bill in a rising one, depending on how the local budgets moved.
Exemptions attach to the owner, not the house
Many states offer homestead exemptions that reduce taxable value for an owner occupying the property as a primary residence, along with exemptions for seniors, veterans and others.
These are generally applied for rather than granted automatically, and they lapse when the qualifying owner no longer holds or occupies the property.
A buyer who does not file loses a reduction the previous owner may have had for years, which widens the gap between the old bill and the new one.
Escrow catches up a year late
Where taxes are paid through a mortgage escrow account, the initial monthly figure is often based on the tax history available at closing.
When the reassessed bill arrives, the escrow account is short, and the servicer both collects the shortfall and raises the ongoing monthly payment.
The result is a payment increase in the second year of ownership that surprises buyers who assumed a fixed-rate mortgage meant a fixed monthly obligation.