Question: How do I count the number of unique months in excel?

Array formula in C17:

=SUM(IF(MATCH(DATE(YEAR(List), MONTH(List), 1), DATE(YEAR(List), MONTH(List), 1), 0)=ROW(List)-MIN(ROW(List))+1, 1, 0)) + CTRL + SHIFT + ENTER

Named ranges
List (A2:A15)
What is named ranges?

Change the named range.

Count unique distinct months.xls
(Excel 97-2003 Workbook *.xls)

IF(logical_test;[value_if:true];[value_if_false])
Checks whether a condition is met, and returns one value if TRUE, and another value if FALSE

MATCH(lookup_value;lookup_array; [match_type] Returns the relative position of an item in an array that matches a specified value

DATE(year,month,day) returns the number that represents the datein Microsoft Office Excel date-time code

MONTH(serial_number) returns the month, a number from 1 (January) to 12 (December)

YEAR(serial_number) returns the year of a date, an integer of the range 1900-9999

SUM(number1,[number2],)
Adds all the numbers in a range of cells

MIN(number1,[number2])
Returns the smallest number in a set of values. Ignores logical values and text

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