A supplementary tax bill is issued by the City and reflects any additions or improvements you have made to your property. 

You receive a supplementary tax bill for one of the following reasons:

Building assessment

• you had some renovations/improvements done to your property that has increased its current value;
• you have constructed a building on the property

Reclassification

• there has been a change in the use of your property resulting in a change in the tax class of your property assessment.

There are two methods of calculating your supplementary taxes:

1. First year supplementary:  The first year, for which a supplementary or omitted assessment is issued, the supplementary taxes are calculated by multiplying the tax rate by the supplementary assessment and applying the most recent level of taxation.   The result is then prorated for the number of days from the effective date.
2. Subsequent year supplementary:  To calculate supplementary taxes for a second or subsequent tax year for a single event, the tax level for the property is recalculated inclusive of the supplementary or omitted assessment.  The supplementary taxes are then calculated by multiplying the tax rate by the supplementary assessment and applying the revised tax level up to a maximum of 100%.

Supplementary taxes for properties with assessment in more than one capped class are calculated independently by class.

Residential and Farmland Awaiting Development Assessment:  Supplementary taxes are calculated by multiplying the tax rate by the supplementary assessment and prorating for the number of days from the effective date.

As a result of a supplementary tax billing, the tax level of a property could be revised for the year of a supplementary and or any subsequent year(s).  Previously billed taxes are recalculated to reflect the revised tax level.

For adjustments to previously billed taxes, see Capping Recalculation, Charge or Credit on your supplementary bill.

Your supplementary taxes are due in three instalments.  If you are currently enrolled in the preauthorized tax program, your supplementary taxes will be withdrawn from your bank account on your next withdrawal dates.  If you wish to enrol in the preauthorized tax program, please call the Customer Service Centre at 3-1-1, or if calling outside the City limits call 905-615-4311 or e-mail at tax@mississauga.ca. 

The Municipal Property Assessment Corporation (MPAC) is responsible for the valuation function of all properties in Ontario.

Under the Assessment Act, MPAC can provide the municipality with assessment values where the assessment has been omitted from the current assessment roll and/or the assessment rolls of either of the two preceding years or when there is an increase in assessment for the current year, for such things as new buildings or additions/improvements.

From the information supplied by MPAC, the City of Mississauga calculates the tax amounts due and issues tax bills.  Until the City receives the information from MPAC, a supplementary tax bill cannot be issued.  Consequently there may be a considerable time lapse from the effective date of the supplementary until you receive a tax bill.

If you think your supplementary assessment is incorrect, a reconsideration process is available through MPAC, for which there is no fee. Visit the MPAC website at the related link above for details on how to request a reconsideration.

You also have the right to appeal to the Assessment Review Board (ARB)which is an independent tribunal. An appeal must be filed within 90 days of the date of the notice of assessment. Visit the ARB website at www.arb.gov.on.ca for all the details on how to file an assessment appeal.

For further information, please call the Customer Service Centre at 3-1-1, or if calling outside the City limits call 905-615-4311 or e-mail at tax@mississauga.ca.