How to Tell If Your MPAC Assessment Is Too High: 7 Signs Worth Checking

Most Ontario homeowners have never checked whether their assessment is fair. Not because it's hard — the tools are free and the check takes an evening — but because nothing prompts them to. The bill arrives, it looks like last year's bill, and life moves on.

That inertia has a price. If your property is assessed high relative to genuinely comparable homes, you overpay every single year, and because Ontario hasn't run a province-wide reassessment since the January 1, 2016 valuation, an error from that model has been compounding for a decade. This is the diagnostic: seven signs that your assessment deserves a closer look, and the method for confirming it.

One ground rule before the list. Your assessment being far below what your home would sell for today means nothing — every Ontario property is valued as of January 1, 2016, so nearly everyone's assessment looks "low" against today's market. Fairness is measured against other assessments, not against sale prices. (If that's surprising, read our explainer on why your assessment and your market value are different numbers first.)

The 7 signs

1. MPAC's file describes a property you don't own

Wrong square footage, a "finished" basement that's bare concrete, a second full bathroom that's actually a powder room, a garage or outbuilding that was demolished, lot dimensions that don't match your survey. Recorded-detail errors are the most common problem and the most winnable, because there's no debate about value judgment — MPAC priced a property that doesn't exist. If you check only one thing on this list, check this.

2. Your assessment per square foot is well above your street's

The cleanest single metric. Divide your assessed value by your above-grade living area, do the same for similar nearby homes, and compare. Similar homes on the same street should cluster; if you sit 10%+ above the cluster, that's a genuine red flag. (The full method is below.)

3. A near-identical home nearby carries a meaningfully lower assessment

Same builder model, same vintage semis, mirror-image side of a duplex — Ontario's suburbs are full of true twins. If your twin is assessed $60,000 below you and neither property has been renovated, one of the two numbers is wrong, and the review process exists to find out which.

4. You recently paid less than the assessed value

During the freeze, almost everyone buys for far more than their 2016-based assessment. Paying less than it inverts the normal pattern and suggests the 2016 number may have been high even for its own date. It's not conclusive on its own — but combined with comparables, it's strong supporting evidence.

5. Your property has problems its assessment ignores

The assessment is supposed to reflect your property's current physical state (at 2016 prices). Structural issues, chronic water damage, a condemned outbuilding, or condition well below the neighbourhood norm are relevant if MPAC's model treated your property as typical. Cosmetic wear doesn't count; documented, value-affecting condition does.

6. Your assessment changed and you don't know why

If you received a Property Assessment Notice mid-freeze, something in your file changed — new construction, a renovation permit, a classification change, a severance. Sometimes the trigger is legitimate but the amount is off: a $40,000 deck addition that raised the assessment $90,000 is worth questioning. Never file the notice away unread; it also starts a 120-day clock if you want to challenge it.

7. You've never once checked

Not a joke. Mass appraisal values millions of properties with a statistical model, and a model that's right on average is still wrong on individuals — some high, some low. The highs don't self-correct during a freeze; they just keep billing. If you've owned since before 2016 and never verified your file, you're trusting a decade-old model output sight unseen.

The confirmation method (one evening, free)

Signs get you suspicious. This gets you an answer.

Step 1 — Pull your file. Log in to MPAC's AboutMyProperty tool with the roll number and access key from your Property Assessment Notice (roll number is also on your municipal tax bill). Verify every recorded detail against reality: living area, lot size, year built, bathrooms, basement finish, structures.

Step 2 — Build a comp set. Using the tool's neighbourhood comparison, select three to five properties genuinely similar to yours: same area, similar size (within ~15%), similar age and style, similar lot. Resist the urge to pick only the lowest-assessed homes — a reviewer sees the same data you do, and cherry-picking kills credibility.

Step 3 — Run the table. For each property: assessed value ÷ living area = $/sq ft. Like this:

Property

Assessed value

Living area

$/sq ft

Yours

$588,000

1,450

$406

Comp 1

$529,000

1,480

$357

Comp 2

$541,000

1,510

$358

Comp 3

$518,000

1,395

$371

Here the subject sits 9–14% above every comparable — a real gap, not noise.

Step 4 — Sanity-check the gap. Before concluding you're over-assessed, ask what could justify the difference: a finished basement the comps lack, a bigger or premium lot (ravine, corner, no rear neighbours), a major addition, superior condition. If honest adjustments close the gap, the system is working. If they don't, you have a case.

How big does the gap need to be?

Rules of thumb, not law:

Under ~5%: within the tolerance of mass appraisal. A challenge is unlikely to succeed or to be worth your evening.

5–10%: judgment zone. Worth pursuing if you have a factual error or unusually clean comparables; the dollar stakes depend on your municipal tax rate.

10%+ with solid comps, or any material detail error: worth challenging. On a $600,000 assessment at a ~0.9% combined tax rate, a 10% over-assessment is roughly $540 a year — recurring until the next province-wide reassessment, whenever that is.

That last point is what makes checking worth the evening: a correction doesn't buy you one year of savings. It resets your baseline for the remainder of the freeze and beyond.

If the check says yes

The fix is a Request for Reconsideration — MPAC's free internal review. You submit your evidence (the detail corrections, your comp table), MPAC reviews and responds, and if you disagree with the outcome you can escalate to the Assessment Review Board. Deadlines are strict: generally March 31 of the tax year, or 120 days from the issuance date if you received a new notice. The complete walkthrough — what to include, how to frame the equity argument, the mistakes that sink reviews — is in our full guide: Is your MPAC assessment too high? The complete Ontario guide.

Frequently asked questions

How long does the check actually take?

For most homeowners: one evening. Pulling your file and verifying details is under an hour; building an honest comp table is one to two more. The RfR itself, if you file one, is a form plus the evidence you've already assembled.

Can I check a property I'm about to buy?

You can research any Ontario property's assessment, and it's smart due diligence — an over-assessment becomes your annual overpayment on closing. Full file access via AboutMyProperty belongs to the owner, so ask the seller for details you can't see.

My comparables aren't identical to my house. Does that ruin the analysis?

No — perfect twins are rare. What matters is that differences are honest and adjusted for in your reasoning. Three imperfect-but-defensible comparables beat one perfect twin and beat ten loose ones. Explain the differences rather than hiding them.

What if my check shows I'm assessed below my neighbours?

Then the freeze is working in your favour and you should do precisely nothing. There's no obligation to report it, and an individual review isn't triggered by staying quiet. This is also why you verify your own details before filing anything — a review of a property with an unrecorded finished basement can move the number the wrong way.

Do I need a lawyer, paralegal, or tax consultant to do any of this?

No. The RfR process is designed for owners to use themselves, filing is free, and residential stakes rarely justify professional fees. Where representation rules do apply is at the Assessment Review Board stage — but you can represent yourself there too, and most residential cases with merit resolve at the RfR stage without ever reaching it.