Is Your MPAC Assessment Too High? The Complete Ontario Guide

The short version: Your Ontario property taxes are based on what MPAC says your home was worth on January 1, 2016 — not what it's worth today. If MPAC's number is high compared to similar homes near you, you're paying more than your fair share, and you have a free, legal way to challenge it: a Request for Reconsideration (RfR). The general deadline is March 31 of the tax year. This guide explains how to check whether you're over-assessed and how to fix it yourself.

First, understand the number on your notice

The Municipal Property Assessment Corporation (MPAC) assesses close to 5.7 million properties across Ontario — the largest assessment jurisdiction in North America. Your municipality takes MPAC's assessed value for your property, applies its tax rate, and that's your property tax bill.

Here's the part that confuses almost everyone: Ontario's assessed values are frozen in time. The last province-wide reassessment used a valuation date of January 1, 2016. A new reassessment was scheduled for 2020, but the province postponed it during COVID and has kept extending the postponement ever since. MPAC has confirmed that assessments for the 2026 tax year are still based on fully phased-in January 1, 2016 values. As of this writing, no reassessment date has been announced, so 2027 is expected to work the same way unless the province says otherwise — we'll update this guide the moment that changes.

So when your assessment says $612,000 and homes on your street sell for $1.1 million, that is not an error. Every property in Ontario is valued as if it sold in 2016. Which leads to the single most important idea in this guide.

"My assessment is lower than my market value" is not the test

Because everything is valued at 2016 levels, your assessment being far below today's market value tells you nothing. Nearly every home in Ontario is assessed below its current market value.

The test that actually matters is equity: is your property assessed high relative to comparable properties near you?

Ontario's property tax system is revenue-neutral by law. Your municipality decides how much total tax it needs, and assessments only determine each owner's share of that total. That has two consequences:

"My taxes are too high" is not a winnable argument. MPAC doesn't set tax rates, and the total your city collects doesn't change based on your appeal.

"My assessment is unfair compared to similar homes" is a winnable argument. If your house is assessed at $650,000 and genuinely comparable houses on your street are assessed at $560,000–$580,000, you are carrying more than your share of the municipal tax burden — every year — and correcting that is exactly what the review process exists for.

What an over-assessment costs you

The math is simple: (excess assessment) × (your total property tax rate).

Say your home is assessed $70,000 higher than comparable neighbours, and your combined municipal + education tax rate is about 0.9%. That's roughly $630 a year you're overpaying. And because Ontario hasn't reassessed since 2016, a correction doesn't just fix one year — your corrected value carries forward until the next province-wide reassessment. A single successful review can be worth several thousand dollars over the life of the freeze.

Residential values across Ontario have risen roughly 94% since 2016, but they haven't risen evenly — some neighbourhoods and property types moved far more than others. The freeze locks in 2016's relative picture, and any errors in it, for a decade.

The three ways properties end up over-assessed

1. Wrong property details. MPAC's records may show more square footage than you have, a finished basement that isn't finished, a garage that was demolished, more bathrooms than exist, or lot dimensions that don't match your survey. Factual errors like these are the most common — and most winnable — basis for a correction, because there's no judgment call involved. MPAC valued a property that doesn't exist.

2. Out-of-line valuation versus comparables. Even with correct details, mass appraisal is a statistical exercise across millions of properties. Some come out high relative to genuinely similar homes nearby. This is the classic equity argument.

3. Missed depreciation or condition issues. The assessment is supposed to reflect your property's current physical state at 2016 prices. If your property has deteriorated, suffered damage, or has issues the model didn't capture (and your neighbours' homes don't share them), the value may be overstated.

How to check whether you're over-assessed (step by step)

Step 1: Pull your property's record

Log in to MPAC's AboutMyProperty tool (aboutmyproperty.ca). You'll need the roll number and access key printed on your Property Assessment Notice. If you can't find a notice, your roll number is on your municipal tax bill, and MPAC can help you get access.

Step 2: Verify every detail

Check what MPAC has on file: total living area, lot size, year built, number of bathrooms, basement finish, garages and outbuildings, and any additions. Measure or check your own documents if you're unsure. Any material discrepancy is grounds for a Request for Reconsideration on its own.

Step 3: Compare against similar properties

AboutMyProperty lets you view information about comparable properties in your neighbourhood, free. You're looking for homes that genuinely match yours: similar size, age, style, lot, and location. Then compare on a like-for-like basis — assessed value per square foot is the cleanest single measure.

A worked example:

Property

Assessed value

Living area

$/sq ft

Your home

$648,000

1,610 sq ft

$402

Comp A (same street, similar age)

$571,000

1,650 sq ft

$346

Comp B (one street over)

$560,000

1,580 sq ft

$354

Comp C (same model, same builder)

$585,000

1,610 sq ft

$363

In this example, the subject home is assessed roughly 12–16% above genuinely comparable properties. That's a meaningful inequity worth challenging — not a rounding difference.

Be honest with yourself at this step. If your comparables have unfinished basements and yours is finished, or they back onto a rail line and you back onto a ravine, the gap may be justified. Weak comparables are the fastest way to lose a review. Three to five strong, honest comps beat ten loose ones.

Step 4: Decide if the gap is worth pursuing

As a rule of thumb, if you're within about 5% of your comparables, the system is working roughly as intended and a review is unlikely to go anywhere. Gaps of 10% or more, supported by solid comparables or a factual error, are worth your time. Between those, it depends on your tax rate and how strong your evidence is.

How to file a Request for Reconsideration (RfR)

The RfR is MPAC's free internal review. No lawyer, no fee, no hearing — you submit evidence, MPAC reviews it and responds.

Deadline — read this carefully:

The general deadline to file an RfR is March 31 of the tax year (for example, the deadline for the 2026 tax year was March 31, 2026).

If you received a new Property Assessment Notice (because something about your property changed), your window is 120 days from the issuance date printed on that notice — which may give you more or less time than March 31. Check the date on your notice.

Miss the deadline and you generally wait for the next tax year. The clock matters.

How to file: online through AboutMyProperty (fastest), or by mailing MPAC's RfR form. Filing is free either way.

What a strong RfR contains:

Your requested value and a one-page explanation of why, in plain language

A comparable-property table like the one above, with addresses or roll numbers

Documentation of any factual errors (measurements, photos, survey, permits)

Photos supporting condition issues, if that's part of your argument

You don't need legal language. You need a clear, evidence-backed story: here is my property, here are genuinely similar properties, here is the gap, here is the value that would be fair.

What happens next: MPAC reviews your request and issues a decision. If MPAC agrees, your assessment is corrected and your municipality adjusts your taxes. If you disagree with the outcome, you can escalate to the Assessment Review Board (ARB) — an independent tribunal. Residential owners generally must file an RfR first before appealing to the ARB. One important note: you can represent yourself at the ARB, but anyone representing you (other than a lawyer or licensed paralegal) runs into Ontario's licensing rules — another reason the do-it-yourself route is the practical one for homeowners.

Common mistakes that sink reviews

Arguing about taxes instead of assessment equity. The review process cannot lower your tax rate. Frame everything as assessment fairness.

Comparing your assessment to sale prices from this year. Today's sales reflect today's market; your assessment reflects January 1, 2016. Comparables must be other assessments, not recent sold prices.

Cherry-picking comparables that don't really match. MPAC's reviewers look at the same data you do. Obvious cherry-picking damages your credibility.

Missing the deadline. March 31 (or your notice's 120-day window). Put it in your calendar now.

Assuming a review can't backfire. If MPAC finds its records understate your property (say, an unrecorded finished basement), a review can theoretically move the number the other way. This is rare, but it's a real reason to verify your details honestly before filing.

Frequently asked questions

Does filing an RfR cost anything?

No. The RfR is free. Escalating to the ARB involves a filing fee, but most residential cases that have merit resolve at the RfR stage.

Will challenging my assessment affect my home's resale value?

No. Your assessment is not your market value, and buyers' agents know it. If anything, lower carrying costs are a selling point.

My neighbour's identical house is assessed lower than mine. Is that enough?

One comparable is a start, not a case. Build a table of three to five. If the pattern holds across several genuine comparables, you have a real equity argument.

What if I just bought my home for less than the assessed value?

A recent purchase price can be relevant evidence, but remember the valuation date: MPAC's number is a 2016 value. A 2026 purchase below the 2016-based assessment is worth flagging, especially alongside comparables.

When will Ontario reassess?

No date has been announced. When it happens, every property in the province gets a new value at once — and given how unevenly values have moved since 2016, millions of owners will see their share of the tax burden shift. Checking your assessment before that day means you enter the reassessment from a correct baseline.