Millions of American homeowners have opened a property tax bill this year and felt sticker shock. It is not their imagination: after home values climbed steeply over recent years, local assessments have been catching up, and the increases are landing now, as Kiplinger reported. Here is what is driving it and, more usefully, what you can do about it.

Why bills are jumping

A property tax bill is based on what your local government thinks your home is worth. When home prices rose sharply, assessed values in many places did not update immediately; assessors re-value on their own cycles, sometimes every few years. When they finally catch up, several years of appreciation can show up in one bill. Add local governments' own budget pressures, for schools, services and rising costs, and the result is higher tax bills.

How much varies enormously by location. Property tax is intensely local: effective rates range from well over 2% of a home's value in the highest states to well under half a percent in the lowest, according to Tax Foundation data. Two identical homes in different states can carry wildly different bills.

The math, in plain English

The formula is simpler than it looks: your bill is your home's assessed value multiplied by the local tax rate.

The "assessed value" is the taxable value your local assessor assigns, often lower than the price your home would fetch on the market. The tax rate is frequently expressed as a "millage rate", where one mill equals $1 of tax per $1,000 of assessed value. Several authorities, your city or town, county, school district and any special districts, each set their own millage, and they add up to your total. As a rough illustration, a home assessed at $300,000 with a combined rate of 15 mills would owe about $4,500 a year.

Four steps to challenge your assessment

If your assessment looks too high, you can usually contest it. The process rewards moving quickly and being organized.

1. Check the notice for mistakes. Your assessment lists your home's details, square footage, bedrooms, lot size, condition. Errors here are among the most common reasons a home is over-assessed. Compare the record against reality; if it lists more space or rooms than you have, that is a concrete basis for appeal.

2. Pull comparable sales. Find recent sale prices of similar homes nearby, same area, size and age. These "comps" are the backbone of an appeal, showing what your property is really worth. Assessor websites and real-estate platforms are good sources.

3. File before the deadline. This is the step people miss. The window to appeal is often short, commonly a matter of weeks after the notice arrives, and varies by jurisdiction. Miss it and you typically wait a full year. Check your notice and your local assessor's site for the exact date and procedure.

4. Make your case. Appeals go to the assessor or a local review board. Many homeowners never bother, yet a meaningful share of those who do win some reduction. Present your evidence, the errors, the comps, calmly and in writing.

Don't leave exemptions on the table

Separately from appeals, many homeowners qualify for exemptions that lower the taxable value, and often fail to claim them. A "homestead" exemption, available in most states, reduces the assessment on your primary residence. There are frequently additional breaks for older homeowners (often from age 65), for veterans, and for people with disabilities, and some places freeze a senior's assessed value so the bill stops rising. These rarely apply automatically; you usually have to apply through your local assessor's office.

Manage the cash-flow hit

Finally, plan for the payment. If you have a mortgage, your lender likely collects property tax through an "escrow" account bundled into your monthly payment; a jump in your assessment can raise that monthly figure, so it is worth knowing it is coming. Without escrow, set money aside for a bill that may be materially larger than last year's.

The broader point is that a rising assessment is not a verdict you simply have to accept. A careful read of the notice, a handful of comparable sales and a timely filing can, in many cases, trim a bill, and the exemptions you are entitled to are worth claiming every year. This article is informational and not tax or financial advice, and property tax rules vary by location.