Every entry below is the rule as Canada publishes it. It is a reference, not a calendar: where a deadline runs from something only you know, this page says so instead of showing a date.
This is the rule as published by the registry, checked against the primary source on the date shown. It is not your filing date. Where a deadline runs from incorporation, from a fiscal year the company itself elects, or from an event only you know about, no date can be derived here at all — the figure you see is the formula, not the answer. Extensions, transitional regimes and entity-specific exemptions are not reflected. Confirm with the registry before you rely on a date.
The corporation sets its own year end. Under subsection 249.1(1) of the Income Tax Act a fiscal period is «the period for which the person's or partnership's accounts … are made up for purposes of assessment», and for a corporation «no fiscal period may end … more than 53 weeks after the period began». So the year follows from how the corporation makes up its accounts, fixed in practice by the first return it files, and once fixed it is not freely moved: subsection 249.1(7) provides that no change in the time when a fiscal period ends may be made without the concurrence of the Minister. Section 249 itself, which defines «taxation year», was not read for this record, and neither was the treatment of a first or final short year. One consequence belongs here rather than in a footnote: the corporate-registry duty below does not run on this clock at all. The annual return to Corporations Canada is counted from the anniversary of incorporation, amalgamation or continuance, so a Canadian corporation lives with two independent annual cycles, and a date computed from one of them is never the date for the other.