MONTH
指定の日付値の月を返します。月は、1 から 12 までの整数として返されます。
This function is part of the Open Document Format for Office Applications (OpenDocument) standard Version 1.2. (ISO/IEC 26300:2-2015)
MONTH(数値)
Number is the internal date number.
MONTH() returns the integer part of the month.
When entering dates as part of formulas, slashes or dashes used as date separators are interpreted as arithmetic operators. Therefore, dates entered in this format are not recognized as dates and result in erroneous calculations. To keep dates from being interpreted as parts of formulas use the DATE function, for example, DATE(1954;7;20), or place the date in quotation marks and use the ISO 8601 notation, for example, "1954-07-20". Avoid using locale dependent date formats such as "07/20/54", the calculation may produce errors if the document is loaded under different locale settings.
Unambiguous conversion is possible for ISO 8601 dates and times in their extended formats with separators. If a #VALUE! error occurs, then unselect Generate #VALUE! error in LibreOffice - PreferencesTools - Options - LibreOffice Calc - Formula, button Details... in section "Detailed Calculation Settings", Conversion from text to number list box.
=MONTH(NOW()) returns the current month.
=MONTH(C4) returns 7 if you enter 2000-07-07 to cell C4 (that date value might get formatted differently after you press Enter).