After return of the assessment roll each year, any assessment changes or errors that relate to an increase in assessment value - for example a new residential unit, new commercial tenant or an improvement to property - are billed for taxes by way of a SUPPLEMENTARY TAX NOTICE. Prior to receiving this Supplementary Tax Notice you would have been sent a "Notice of Supplementary or Omitted Assessment" from the Ontario Property Assessment Corporation which contained details of the supplementary assessment.
A new residential unit is assessed for taxation as per the date the unit is ready for occupancy. In most cases, during the first year of occupancy, the land is billed for taxes by an Interim and Final Tax Notice and the unit is billed for taxes by a Supplementary Tax Notice. The following year, the assessment for the land and the unit should be combined and then only an Interim and Final Tax Notice will be issued. Supplementary Tax Notice(s) may be issued with effective dates for the current taxation year and/or the two prior taxation years.