How Property Tax Is Calculated — and Why Yours Went Up

The whole thing is two numbers multiplied

At its core, a property tax bill is:

taxable value × tax rate = the bill

That's it. Everything complicated is complication inside one of those two numbers. And critically, they are set by different people at different times for different reasons — the assessor decides value, elected bodies decide rates. Your bill can rise because either moved, or both.

The layering matters practically. The single largest line on many residential bills is the school or education levy, decided by a body separate from the city council people usually blame. Reading which line grew tells you where to direct the question.

Assessed value is not market value

This is the single biggest source of confusion, and it has three separate causes.

First, it's an estimate made in bulk. An assessor values thousands of properties, usually with a statistical model based on sales of comparable homes, sometimes without ever going inside yours. It is not an appraisal.

Second, it may be dated. Many places reassess on a cycle — every few years rather than annually. Between reassessments, your assessed value doesn't track the market at all, which is why a reassessment year can produce a jump that feels like it came from nowhere. The value didn't leap; the measurement caught up.

Third, many systems tax only a fraction of it. An assessment ratio (or similar mechanism) means a home assessed at some value is taxed on a defined percentage of it. Where this applies, comparing your assessed figure to a neighbouring district's is meaningless unless the ratios match.

One consequence worth stating plainly: what you paid for the house is evidence of value, not the value itself. In some systems a sale does trigger a reassessment to the sale price; in others it explicitly does not. Which one applies to you is a local rule and it changes everything about what to expect after buying.

The rate is really several rates

Rates go by different names — millage, mill rate, tax rate, precept, levy — but the mechanism is usually the same, and it's the reverse of what most people assume.

Typically a taxing body decides how much money it needs (its levy), then divides that by the total taxable value in the district to get the rate. The budget is the input; the rate is the output.

This produces a genuinely counter-intuitive result that explains a lot of angry conversations:

• If every property in the district rises in value equally, and the budget doesn't change, the rate falls and your bill stays roughly flat. Rising values alone do not raise revenue.
• Your bill rises when your value rises faster than the district average — you now hold a larger share of the pie — or when a budget grows, or when a new levy is added.

So "house prices went up, so my taxes went up" is only half right. What matters is your value relative to everyone else's, and what the budgets did.

Why the bill went up

Work through these in order; the bill itself usually tells you which one it was.

1. A reassessment year. Several years of market movement land in one adjustment. The biggest single cause of shock increases.
2. Your value rose faster than the average. Neighbourhood-specific appreciation shifts the share of the total burden onto you even with flat budgets.
3. A budget increased. Some taxing body needed more, so its rate went up. Check which line grew.
4. A new levy or bond was approved. Often voted on in an election most people didn't follow, and it appears as a new line rather than a bigger old one.
5. An exemption ended. A temporary reduction expired, an eligibility condition changed, or a renewal wasn't filed. This one is quiet and common.
6. You improved the property. Permitted work — an extension, a finished basement, a new structure — typically triggers reassessment of the improved portion.
7. A cap reset when the property changed hands. Where value caps exist, they frequently reset on sale. See below.

Two practical notes. If it's a reassessment year, that fact is usually stated on the notice. And if the bill is paid through your mortgage, the increase reaches you as a changed monthly payment months later — see why mortgage payments change.

Why your neighbour pays less

Two near-identical houses on the same street paying very different amounts is normal, and there are five ordinary explanations before you reach "someone made a mistake".

That last point deserves expanding, because it's the most actionable thing in this whole subject. Assessors hold a record card for your property: square footage, bedrooms, bathrooms, lot size, year built, condition, whether there's a basement or garage. That record is often simply inaccurate — it may describe a previous structure, an unbuilt extension, or a mismeasurement.

Requesting your record card and checking it against reality costs nothing, and a factual correction is usually a separate, simpler process than a value appeal.

Exemptions and caps

Most systems reduce the burden for certain owners or circumstances. Common categories:

• A primary-residence reduction for the home you actually live in — variously called a homestead exemption or principal residence relief. Second homes and rentals usually don't get it, and sometimes pay more.
• Age, disability or veteran status reductions.
• Income-based relief in some jurisdictions.
• Agricultural, conservation or historic use valuations, which tax land on its use rather than its development potential.

Two mechanical points that cost people real money. First, many exemptions must be applied for, not granted automatically, and some must be renewed. People commonly qualify for years without claiming. Second, an exemption often doesn't move when you do — buying a home from someone who had one doesn't give you theirs, which is a frequent nasty surprise in a first bill after purchase.

Caps are a different mechanism: a limit on how much the taxable value (or the bill) can rise in a year. Where they exist, they create a gap between assessed and taxable value that grows the longer you own — which is the main reason a long-term neighbour pays far less for an identical house. And because caps commonly reset on sale, a buyer can inherit a bill dramatically higher than the seller's, even with no change to the property. Estimating your future bill from the seller's current bill is, in those systems, a serious mistake.

How an appeal actually works

Appeals exist in most systems, and understanding what they're for determines whether yours goes anywhere.

You appeal the assessed value, not the tax rate and not the amount. Rates are set by elected bodies through a budget process; that's a political question, not an appeal question. The appeal asks one thing: is the assessor's valuation of this property wrong?

What that means in practice:

• "My taxes are too high" is not a ground. "This property is assessed above its market value" is. So is "comparable properties are assessed lower."
• Evidence that works: recent sales of genuinely comparable properties, assessments of similar nearby homes, an independent appraisal, photographs of defects that reduce value, and factual errors on the record card.
• The deadline is short and strict. It typically runs from the date of the assessment notice — not the tax bill, which arrives much later. Missing it usually means waiting a full cycle.
• There's often an informal stage first — a conversation with the assessor's office — that resolves many cases, particularly factual errors, without a formal hearing.
• It can go up. In some jurisdictions a review can increase the assessment. Worth knowing before filing.

A note of caution on companies offering to appeal on your behalf for a share of the savings: they're legitimate in many places, but read what happens if the appeal fails, what the fee is calculated on, and how long the agreement binds you. Anything arriving unsolicited right after an assessment notice deserves the same scepticism as any other unsolicited approach — see how to check whether a site is genuine.

What people get wrong

• "It's based on what I paid." Sometimes a sale triggers reassessment, often it doesn't. Local rule.
• "Home values rose, so revenue rose." Usually the rate falls to offset. What moves your bill is your value relative to the district, and the budgets.
• "I'll appeal the amount." You appeal the valuation. The amount follows from valuation and rate, and rates aren't appealable.
• "The seller paid this much, so I will too." Where caps reset on sale, this can be badly wrong in your first year.
• "I don't need to apply for the exemption." Many require an application, and some require renewal.
• "My mortgage covers it, so it's not my problem." An escrow account pays it, but you fund the escrow, and shortfalls come back as a higher monthly payment.
• "The assessor knows what my house is like." Frequently they don't. The record card is worth reading.