To calculate your annual property tax, take your home’s fair market value, multiply it by your local assessment ratio, subtract any exemptions you qualify for, and multiply the result by your millage rate divided by 1,000. Written as one equation: (Assessed Value − Exemptions) × (Millage Rate ÷ 1,000) = Annual Property Tax. Each input comes from a different source. The assessor sets the market value, state or local law fixes the assessment ratio, you apply for exemptions, and elected officials approve the millage rate each year. Once you have the four numbers, the arithmetic takes a minute.
A worked example makes the shape of it clear. A home with a fair market value of $350,000 in a jurisdiction that assesses residential property at 40 percent has an assessed value of $140,000. Subtract a $25,000 homestead exemption and the net taxable value is $115,000. Apply a combined millage rate of 25 mills — that is, 0.025 — and the annual tax comes to $2,875.
Fair Market Value and the Assessment Ratio
Fair market value is the assessor’s estimate of what your home would sell for in a normal transaction between a willing buyer and a willing seller. Local assessors reach this figure through mass appraisal, running statistical models over hundreds or thousands of recent sales rather than inspecting each home every year. For most residential property, the sales comparison approach dominates: the assessor looks at recent sale prices of similar homes nearby and adjusts for differences in size, condition, lot, and features. The cost approach — what it would take to rebuild the home at current prices, minus depreciation — is more common for unusual properties without good comparables. A third method, the income approach, applies mainly to commercial and rental property.
You’ll find your home’s market value on the annual assessment notice from your local appraisal office. Most jurisdictions also keep a searchable online database of current and historical valuations.
Most places don’t tax the full market value. They apply a fixed percentage — the assessment ratio — to convert market value into assessed value. Ratios vary widely: 10 percent in some jurisdictions, 40 percent in others, 100 percent in a few. Residential and commercial property often carry different ratios. Your county assessor’s website or tax office can tell you the ratio that applies to your home. Multiply market value by that percentage to get the assessed value that feeds the rest of the calculation.
If the Assessed Value Looks Wrong
You can appeal an assessment you believe is too high. Deadlines are printed on the assessment notice and are typically at least 30 days out; filing fees generally run from roughly $50 to $175. Disagreeing with the number isn’t enough on its own. The evidence that carries weight includes recent sale prices of comparable homes, an independent appraisal from a licensed appraiser, and photos or documentation of condition problems the assessor may have missed.
Subtracting Exemptions
Exemptions reduce the assessed value before the tax rate is applied, so every dollar of exemption is a dollar the millage rate never touches. The most common is the homestead exemption for a property you own and live in as your primary residence. Additional exemptions target specific groups:
- Senior citizen exemptions, often kicking in at age 65.
- Disability exemptions for homeowners with qualifying disabilities.
- Veteran exemptions, frequently with larger reductions for service-connected disabilities.
Amounts range from a few thousand dollars to $25,000, $50,000, or more, depending on the program. You generally have to apply through your local tax office by a set deadline, often early in the year, and provide documentation such as proof of residency, age, or a military discharge. Once approved, most exemptions renew automatically as long as your ownership and residency don’t change. The savings are worth pursuing: a $25,000 exemption in an area with a 25-mill rate cuts $625 off the annual bill.
The Millage Rate
The millage rate is the tax rate applied to your net taxable value. One mill is one dollar of tax per $1,000 of assessed value, the same as one-tenth of one percent. A rate of 25 mills means $25 for every $1,000. To use the rate in the formula, divide it by 1,000 — 25 mills becomes 0.025 — and multiply by the taxable value.
Your total millage rate is almost never a single number set by a single body. It’s the sum of rates set separately by the county, the city, the school district, and often a library system, a fire district, and other local authorities. Each holds its own budget hearings and sets its own rate, and the combined rate is what appears on your bill. Total rates commonly land in the 15-to-30 mill range but can run higher or lower.
You can pull the current rate from your most recent tax bill, your county tax commissioner’s website, or the local government’s annual budget documents. Because rates can move each year with local spending, use the current year’s number when you’re estimating what you’ll owe next.
Running the Calculation
With all four inputs in hand, the calculation runs in three steps.
- Multiply fair market value by the assessment ratio to get the assessed value. A $350,000 home at a 40 percent ratio has an assessed value of $140,000.
- Subtract exemptions. A $25,000 homestead exemption on that $140,000 leaves a net taxable value of $115,000.
- Multiply by the millage rate divided by 1,000. At 25 mills, $115,000 × 0.025 = $2,875.
When the official bill arrives, check the assessed value, exemption amounts, and millage rate on the statement against your own numbers. Any discrepancy in a single component can inflate the bill, and it’s worth a call to the assessor’s office to resolve.
Charges That Fall Outside the Formula
Your tax bill may include lines that aren’t produced by the millage-rate calculation, so factoring them in separately keeps your estimate honest.
Special assessments pay for improvements or services that benefit specific properties rather than the community at large. Common examples are new sewer lines, sidewalks, drainage, or road paving; ongoing charges for street lighting or landscaping; and community facilities district fees in newer developments that fund schools, parks, or fire stations. Because these charges are tied to benefit rather than value, two neighboring homes with very different market values can owe the same amount. Special assessments may be one-time (sometimes spread over several years of payments) or annual.
Supplemental tax bills often follow a home purchase. The assessor’s records may still show the previous owner’s assessed value, which can be well below what you paid. Once the property is reassessed, many jurisdictions issue a supplemental bill for the difference, prorated from your closing date through the end of the tax year. These bills can arrive months after closing and are separate from the regular annual bill. If the reassessment comes in lower than the prior value, a supplemental refund is possible instead.
Proration at closing divides the current year’s tax between buyer and seller by the number of days each owned the property, usually at a daily rate based on the annual bill. The split appears on the closing disclosure as a credit to the buyer and a charge to the seller, so the amount you actually pay in the year you buy or sell won’t match a full-year calculation.
Everything else on the bill — the ad valorem portion that funds general local government, schools, and the other taxing authorities — is what the formula at the top of this article produces. Verify the four inputs, run the arithmetic, add any special assessments separately, and the total should match.