Generally, when the word month is used in the context of a legal deadline, it means a calendar month.
In the 3rd edition of Halsbury's Laws of England, volume 37, the authors wrote:
"When the period prescribed is a calendar month running from any arbitrary date the period expires with the day in the succeeding month immediately preceding the day corresponding to the date upon which the period starts: save that, if the period starts at the end of a calendar month which contains more days than the next succeeding month, the period expires at the end of the latter month."
The 4th edition of Stroud's Judicial Dictionary includes this:
"[I]n computing time by calendar months, the time must be reckoned by looking at the calendar and not be counting days. Therefore, one calendar month's imprisonment is to be calculated from the day of imprisonment to the day numerically corresponding to that day in the following month, less one....
"So, as regards the requirement of a calendar month's notice of action, in considering what is the length of a calendar month, it is sufficient, when months are broken whatever be the length of either, to go from one day in one month to the corresponding day in the other."
In McCombie, the Court adopted the following words, which are identical to the definition in Jowitt's:
"Calendar month (means) a period of time consisting of thirty days in April, June, September and November, and of thirty-one days in the remainder of the months, except February, which consists of twenty-eight days, except in leap-year, when the intercalary day is added, making twenty-nine days....
"I cannot accept the proposition that a portion of a month is a calendar month...."
In a 1917 Florida case, State v White, Justice Ellis of the Supreme Court of Florida wrote:
"[A] calendar month (means) that period of time elapsing between a given date and the corresponding date of the next preceding month by name."
- Duhaime, Lloyd, Legal Definition of Calendar Day
- Duhaime, Lloyd, Legal Definition of Calendar Quarter
- Duhaime, Lloyd, Legal Definition of Calendar Week
- Duhaime, Lloyd, Legal Definition of Calendar Year
- Kayelle Management v Minister of National Revenue,  1 C.T.C. 271 and at 94 D.T.C. 6116 (FCA)
- McCombie v R.,  4 C.T.C. 2251
- Pelletier v Nolet, 28 N.B.R. (2d) 668, 63 A.P.R. 668 (NBQB, 1980)
- Ruan Transport Corp. v. Peake Inc., 163 Neb. 319, 79 N.W.2d 575 (Nebraska, 1956)
- Smith v Minister of National Revenue,  2 C.T.C. 2454 (TCC)
- State v White, 74 So. 486 (Florida, 1917)