Millions of homeowners are opening their county assessment notices this spring and finding a number that looks nothing like what Zillow says their house is worth.
In many metro areas, taxable values jumped 10% to 30% in a single year even as home sale prices flattened or slipped.
That gap is confusing, frustrating, and in some cases financially painful.
County assessors typically set values using sales data from the prior year or two, so they're often chasing a market that has already cooled.
If your area saw a buying frenzy in 2022 or 2023, that spike can still be baked into your 2025 tax bill.
Your assessment is only half the equation.
Local governments divide their budget needs by the total taxable value in the district, which sets the rate per $1,000 of value.
When assessments rise across the board, officials sometimes leave the rate alone and pocket the difference — a quiet tax increase that doesn't require a vote. **Where the pain is worst** Texas, Florida, and parts of Georgia and Arizona have seen some of the sharpest jumps because they rely heavily on property taxes and have no state income tax to fall back on.
In Florida, homestead exemptions and the 10% assessment cap offer some protection, but non-homestead properties and new buyers can get walloped.
New Jersey and Illinois remain the highest effective property tax states, with average rates above 2%.
A $400,000 home in those states can run $8,000 or more per year. **What you can actually do** You have a window — usually 30 to 90 days from the notice date — to file an appeal.
Miss it and you're stuck until next year.
Start by pulling your property's record card from the county assessor's website.
Look for errors: wrong square footage, a bedroom count that's off, a pool you don't have, or a garage listed as finished when it isn't.
Roughly a third of appealed properties win some reduction, and clerical errors are the easiest cases.
Next, find three to five comparable sales in your neighborhood that closed around the assessment date.
Your county usually publishes its own comps.
If those homes sold for less per square foot than yours is assessed at, you have a case.
You don't need a lawyer for a standard appeal.
Some homeowners hire appraisal firms or tax protest companies that work on contingency, often taking 30% to 50% of the first year's savings.
That can be worth it for commercial property or big commercial-style homes, but for a typical single-family house, the math often favors doing it yourself. **The homestead exemption most people miss** If you bought your home last year and haven't filed for a homestead exemption, you could be leaving hundreds to thousands of dollars on the table.
Florida's exemption, for example, knocks $50,000 off the assessed value, plus additional caps on annual increases.
Texas raised its homestead exemption to $100,000 in recent years.
Deadlines are usually March 1, but many counties grant extensions for new buyers. **Watch for this trap** Some counties automatically raise assessments but won't lower them when the market falls.
If you think your value dropped, you can appeal downward too — and that's worth doing in cooling markets like Austin, Boise, and parts of coastal California.
Our take: an assessment notice is a starting offer, not a final bill, and counties count on most people ignoring it.
Spending an hour gathering comps and filing an appeal is one of the highest-return chores a homeowner can do.
Final Thoughts
The worst outcome is that nothing changes — but the best one can save you four figures a year, every year.