You pay one bill, issued by your city, but it collects for three levels.

The local municipal portion funds your city: roads, parks, libraries, fire services, recreation centres, snow clearing, bylaw enforcement, planning. Each city sets this rate itself through its own budget.

The regional portion funds York Region services shared across all nine municipalities: regional roads, police, public health, water and wastewater, waste management, paramedic services and social services. This rate is set by the Region and applies across it.

The education portion is set by the province, not by your city or the Region, and it funds schools. Your city collects it and passes it on.

This structure explains something that confuses new homeowners. When your bill goes up, it is not necessarily because your city increased spending. The regional or education portion may have moved, or your assessment may have changed relative to others.

Assessed values in Ontario are determined by the Municipal Property Assessment Corporation, a provincial body independent of your municipality. Your city applies a rate to the value MPAC provides. It does not set that value.

MPAC assesses residential property on what it would have sold for on a specified valuation date, considering factors such as location, lot size, living area, age, quality of construction and major improvements. Assessments are intended to be updated periodically, and those updates have been postponed, meaning current assessments reflect an earlier valuation date rather than today's market. The current position and valuation date should be confirmed with MPAC directly, since this has changed more than once.

Two practical consequences. First, buying a home does not automatically reset its assessment to what you paid, so a newly purchased property may be assessed well below its sale price. Second, a renovation or addition that required a permit can trigger a reassessment, which is one more reason unpermitted work causes complications later.

You can look up your own property's assessment details through MPAC, and as a homeowner you can see how it compares with others.

Thornhill is not a municipality of its own. It is a community split along Yonge Street, with the eastern side in the City of Markham and the western side in the City of Vaughan.

That means two Thornhill addresses can be in different cities, paying different local tax rates, dealing with different city halls, and subject to different bylaws on things like permits and secondary suites. Both remain in York Region, so the regional portion is the same.

If you are comparing two Thornhill listings, confirm which municipality each one is in before comparing anything municipal. The address alone will not tell you. Our guide to Thornhill explains the split in full.

Homeowners who believe their assessment is inaccurate can ask MPAC to review it through a Request for Reconsideration, which costs nothing to file. If you remain dissatisfied, there is a further appeal route to a provincial tribunal.

There are deadlines, and they matter. Check the current deadline and process with MPAC rather than assuming, because missing it generally means waiting for the next cycle.

The argument that works is comparison. If similar properties nearby are assessed lower, or if MPAC's records of your property are factually wrong about living area, lot size, finished basement or condition, those are the grounds worth raising. Arguing simply that the figure feels too high is not.

One caution: a review looks at whether the assessment is correct, which means it can go up as well as down. Check your facts before you file.

1. The actual annual amount. Listings usually state it. Confirm the figure and the year it relates to, because an older figure understates the current one.

2. Which municipality the property is in. Obvious almost everywhere, genuinely not obvious in Thornhill.

3. The assessed value. If it is far below the asking price, understand that this does not mean your taxes will stay low forever, and that assessment updates have been postponed rather than cancelled.

4. Whether recent work was permitted. A finished basement or addition done with permits is usually reflected in the assessment. One done without may not be, with other consequences attached. Our guide to legal secondary suites covers those.

5. Whether it is a new build. New construction is often billed on land only until the building is assessed, after which a supplementary bill arrives covering the period since occupancy. Budget for it, because it catches new-home buyers every year.

Property tax is split between buyer and seller based on the closing date and appears on the statement of adjustments. If the seller has paid beyond closing, the buyer reimburses them for the balance of the year. If the seller is behind, the reverse applies.

Your lawyer handles this, but it is worth knowing it exists, because it affects the cash you need on closing day. Our first-time buyer guide covers the other closing costs.

Afterwards, decide how you want to pay. Most cities offer instalments and a pre-authorized monthly plan, and if your mortgage lender collects taxes with your payment they remit on your behalf. Either way, set it up promptly after closing, since late payment attracts charges.

Programs exist that can reduce or defer property tax for certain homeowners, commonly including seniors and people with disabilities on lower incomes, and in some cases relief where a property has been substantially damaged or unusable.

Eligibility, amounts, application deadlines and which level administers them vary between municipalities and change, so none are described in detail here. They are also not well publicized, which means people who qualify frequently do not apply.

If you are a senior homeowner on a fixed income, or helping a parent who is, it is worth a phone call to the city. For families weighing whether a parent can afford to stay in a long-held home, this belongs in the calculation. Our downsizing guide covers that wider decision.