Property tax basis is the dollar value the assessor uses to calculate what you owe
Property tax basis is the assessed value of your property — the number your local assessor decides your home or land is worth. Your property tax bill is calculated by multiplying this basis by your local tax rate. If your assessor sets your basis at $300,000 and your tax rate is 1.2%, you owe $3,600 that year. The basis changes when the property transfers ownership, when you make major improvements, or when the assessor revalues properties in your area.
The basis is not the same as what you paid for the property, what a real estate agent says it is worth, or what you could sell it for today. It is a separate number that exists only for tax purposes. Different states and counties use different methods to set the basis, and some allow you to lock in a lower basis under certain conditions.
Key Takeaways
- Property tax basis is the assessed value your local assessor assigns to your property, and your annual tax bill is this number multiplied by your local tax rate.
- The basis usually changes when you buy the property, make major renovations, or when the assessor conducts a general revaluation of properties in your area.
- Some states cap how much the basis can increase each year, while others allow it to jump to current market value when the property sells.
- You can challenge the basis through your assessor's office or a formal appeal process if you believe the valuation is too high.
How the basis is set when you buy a property
When you purchase a property, the assessor typically uses the sale price as the starting point for the basis. This is called the acquisition value or purchase price basis. If you buy a house for $400,000, the assessor will usually set your initial basis at or near $400,000.
However, some states use a different approach. In states with Proposition 13-style laws (California, Massachusetts, and a few others), the basis is locked in at the purchase price and can only increase by a small percentage each year — typically 2% or less — until the property sells again. In states without this cap, the basis can jump to the current market value whenever the assessor decides to revalue your property, which may happen every year or every few years depending on your county.
What changes the basis after you own the property
The basis can increase if you add significant improvements to the property. A new roof, an addition, a finished basement, or a new driveway may trigger an increase. The assessor will add the estimated cost of the improvement to your basis. A kitchen renovation costing $50,000 might raise your basis by $50,000, though the exact amount depends on how the assessor values the improvement.
The basis can also change during a general reassessment, when the assessor revalues all or many properties in your area. This happens on a schedule set by your county — some reassess every year, others every three to five years. During a reassessment, your basis may go up or down depending on current market conditions and comparable sales in your neighborhood.
In some cases, the basis can decrease. If you own a property in an area where values have fallen, or if you successfully challenge your assessment, the assessor may lower your basis.
How basis differs by state and county
The rules for how basis works vary significantly by location. The table below shows how three common approaches differ:
| Approach | How Basis Is Set | How It Changes | Example States |
|---|---|---|---|
| Capped increase | Purchase price at time of sale | Can increase only 2% per year until property sells again | California, Massachusetts, Florida (homestead) |
| Annual reassessment | Current market value | Reassessed every year to current market value | New York, Illinois, Texas |
| Periodic reassessment | Current market value | Reassessed every 3–5 years to current market value | Pennsylvania, Ohio, Michigan |
You need to know which approach your county uses because it affects how much your tax bill will rise over time. In a capped-increase state, your basis may stay far below market value for decades. In an annual reassessment state, your basis tracks the market closely and your taxes can jump significantly if your neighborhood appreciates.
How to find out what your basis is
Your property tax basis appears on your annual property tax bill or assessment notice. The notice usually lists the assessed value, which is the basis. You can also contact your local assessor's office — they maintain public records of all assessed values in your county. Many counties now post assessment data online, searchable by address.
If you do not receive a bill or notice, you can visit your county assessor's office in person or call them to request your assessment record. Some counties charge a small fee for copies, though viewing the record is usually free. The assessor's office can also explain how they arrived at your basis and what factors they considered.
Challenging your property tax basis
If you believe your basis is too high, you can file a formal challenge called an assessment appeal or tax assessment protest. The process and important date vary by county, but most counties allow you to file between 30 and 90 days after you receive your assessment notice.
To support your appeal, you can gather evidence such as recent appraisals, comparable sales in your area, photographs of property damage or deferred maintenance, or a professional assessment. The assessor's office can tell you what evidence they will accept. Some counties hold informal hearings where you can present your case directly; others require you to submit written documentation. If you disagree with the outcome, you may be able to appeal to a county board of review or take the case to tax court, though this usually requires an attorney.
How basis affects your long-term tax bill
The basis system creates very different outcomes depending on where you live. In a capped-increase state, a homeowner who bought in 1990 for $150,000 might have a basis of only $250,000 today even though the house is worth $800,000. In an annual reassessment state, that same house would have a basis close to $800,000, and the owner would pay taxes on the full current value.
This matters because it determines how much your property taxes will rise as your neighborhood appreciates. If you are considering moving to a different state or county, understanding the basis rules can help you estimate your future tax liability. It also affects the financial impact of home improvements — in a capped-increase state, adding a $100,000 kitchen may have little effect on your taxes, while in an annual reassessment state, it could increase your basis significantly.
Frequently Asked Questions
Is property tax basis the same as the purchase price?
Usually it starts at the purchase price, but it is not always the same. The assessor may adjust it based on the condition of the property or comparable sales. After purchase, the basis can change due to improvements, reassessments, or appeals. In some states, the basis can stay below the purchase price if the market declines.
Can I lower my property tax basis?
Yes, through an assessment appeal if you can show the assessor overvalued your property. You will need evidence such as a recent appraisal, comparable sales data, or documentation of property damage. The assessor's office can explain the appeal process and important date in your county.
What happens to my basis if I make home improvements?
Major improvements typically increase your basis. The assessor will add the estimated value of the improvement to your current basis. Minor repairs and maintenance usually do not change the basis. The assessor can tell you which improvements trigger a reassessment in your area.
Does my basis reset if I refinance my mortgage?
No. Refinancing does not change your property tax basis. The basis is tied to the property itself, not to your loan. Only a sale, major improvement, or reassessment by the assessor will change it.
Why is my neighbor's basis lower than mine if we own similar houses?
Neighbors can have very different bases if they bought at different times, made different improvements, or live in a state with capped increases. In a capped-increase state, someone who bought decades ago will have a much lower basis than someone who bought recently, even if the houses are identical and worth the same today.