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Supplementary tax bill

If you’ve made additions or improvements to your home or business property, it might change the value of your property as assessed by the Municipal Property Assessment Corporation (MPAC). The City will issue a Supplementary tax bill that will reflect the change in your property tax amount as a result of changes in your property value.


If your home is newly constructed you’ll also receive a supplementary tax bill based on the value of the property as assessed by MPAC. This will reflect the tax amount for your property value from the effective occupancy (closing) date.


When is a supplementary tax bill issued

You’ll receive a supplementary tax bill if:

  • Your house was recently built and when you purchased it, it was only assessed for vacant land
  • A new building was constructed on your business property
  • You made renovations or improvements such as an extension, pool, or separate out buildings that increased its market value
  • The use of all or part of your property has changed, resulting in a change to your tax class

If you own a new home, your supplementary tax bill will reflect the assessed value of your home from the date you occupied it (closing date).

Since the City can issue a supplementary tax bill only after receiving the property assessment information from MPAC, you will receive your supplementary tax bill after the effective date of your supplementary assessment value.

Supplementary taxes are calculated for all applicable years.

Paying your supplementary taxes

Your supplementary taxes are due in three instalments. If you’re currently enrolled in the pre-authorized tax program, your supplementary taxes will be withdrawn from your bank account automatically.

If you wish to enrol in the pre-authorized tax program, please call 311 (905-615-4311 outside City limits) or e-mail us at


Changes to tax level for business taxes

Your supplementary assessment can change the tax level of your property. If a tax bill has already been issued, taxes will be recalculated to reflect your revised tax level. The “Capping Recalculation, Charge or Credit” section of your supplementary bill will show any adjustments to previously billed taxes.

Calculation of business supplementary taxes

First year

In the first year when the supplementary assessment is issued by MPAC, supplementary taxes are calculated by multiplying the tax rate by the supplementary or omitted assessment value and applying the most recent level of taxation. The amount is then prorated for the number of days from the effective date.

Subsequent year

Supplementary taxes for the second and subsequent tax year are determined by first recalculating the tax level of the property inclusive of the supplementary or omitted assessment value.

The tax rate is then multiplied by the supplementary assessment and the result is applied to the revised tax level up to a maximum of 100%.


Supplementary taxes for Residential and Farmland awaiting development assessment are calculated by multiplying the tax rate by the supplementary assessment. The amount is then prorated for the number of days from the effective date.


Reconsidering supplementary property value assessment

If you think your supplementary property assessment is incorrect, you can submit a request for reconsideration to MPAC. You also have the right to appeal to the Assessment Review Board (ARB) within 90 days of the date of the Notice of Assessment from MPAC.


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