How property tax actually works
A plain-English walkthrough of assessed value, mill rates, exemptions, and why two identical homes can owe wildly different bills.
Property tax is one of the oldest forms of taxation in the United States, older than the federal income tax by more than a century. Yet most homeowners understand it only vaguely — you pay it, it's on your tax bill, it's part of your mortgage escrow. Actually understanding it unlocks real savings.
The basic formula
Every property tax bill in the country comes down to two numbers multiplied together:
Annual tax = Assessed value × Tax rate
That's it. The complexity comes from what "assessed value" actually means and how "tax rate" is expressed.
What is "assessed value"?
Your home's assessed value is what the county says it's worth for tax purposes. It's almost always different from what it would sell for on the market, and different from what a lender would loan against it.
Most counties apply an assessment ratio — a fraction of market value used for tax purposes. Examples:
- Full-value states (like California): assessed value ≈ market value, but with caps (Prop 13 limits annual increases to 2%)
- Fractional-value states: assessment ratio of 30–80% of market value (common in much of the Midwest and South)
- Equalization states: assessor sets a raw value, then a state-level equalization factor adjusts it
Your assessment notice — often called a "notice of valuation" or "appraisal notice" — arrives annually (sometimes less often) and is your legal starting point for challenging the number.
What is a "mill rate"?
A mill is one one-thousandth of a dollar. A mill rate of 18.5 means you pay $18.50 per $1,000 of assessed value.
Mill rates are usually the stack of all the taxing authorities with jurisdiction over your property. On a single tax bill, you might see:
- County general fund: 5.2 mills
- City operating: 7.8 mills
- School district: 14.1 mills
- Fire protection district: 0.9 mills
- Library district: 0.4 mills
- Total: 28.4 mills
Not every state uses the word "mill." Some say "tax rate per $100" (divide mill rate by 10) or "effective rate" (multiply by 0.1%). The math is the same.
How exemptions change the bill
An exemption subtracts a specific dollar amount or percentage from your assessed value before the tax rate is applied. Common exemptions include:
- Homestead exemption: reduces the taxable value of a primary residence. Every state has some version; amounts range from ~$5,000 to $100,000+.
- Senior exemption: additional reduction for homeowners 65+
- Disability exemption: for permanently disabled homeowners
- Veteran exemption: for military veterans (rules vary widely)
- Agricultural/conservation: for land in productive use
Most exemptions require you to file paperwork with your county. Many are a one-time filing that rolls over automatically. Many homeowners fail to claim exemptions they qualify for — it's one of the single highest-ROI moves in property tax management.
Why two identical homes can owe different amounts
Two identical homes on opposite sides of a county line can easily owe 2–3× the property tax of each other. Why?
- Different mill rates (different stacked taxing authorities)
- Different assessment years (one reassessed recently, one not)
- Different exemption status (one owner is senior, other isn't)
- Special assessment districts (one is inside a CDD, the other isn't)
- Historical abatements or incentives (property got a 5-year abatement from an economic development district)
Why your bill goes up even when rates don't
Local governments often say "we didn't raise the tax rate" when bills go up. Both statements can be true. Your bill can rise without a rate hike because:
- Reassessment captures market appreciation (your home's taxable value went up)
- Cap/exemption phase-outs (Florida's Save Our Homes cap lifts when you sell)
- Added special assessments (bond measure, infrastructure district)
- New improvements on your property (addition, pool, new roof permit)
What you can actually control
You can't lower the mill rate; that's set by your local legislative bodies. But you can:
- Claim every exemption you qualify for (see our homestead savings tool)
- Appeal an inaccurate assessed value (see our appeal savings tool)
- Relocate to a lower-burden jurisdiction (see our relocation calculator)
- Watch reassessment notices carefully and challenge errors quickly
The rest of the math — your current bill, savings from an exemption, impact of an appeal — is what the calculators on this site are for. Start with the mill rate calculator if you know your rate, or the effective rate calculator if you just have your current tax bill and home value.