This Excel lambda function calculates the growth that a current month's value represents when compared to an arbitrary number of months prior to the current month

excel-lambda-GROWTHFROMOFFSET.txt

/*
GROWTHFROMOFFSET

Calculates the growth that a current month represents when compared
to the same measure an arbitrary number of months ago

Inputs:
	- month_col: a Table column, a cell range (using absolute references) or an array containing the months formatted as dates
	- value_col : a Table column, a cell range (using absolute references) or an array containing the values
	- month_offset : the number of months prior to the month on the current row that you want to compare with
  - [if_error] : an optional value to return in case of error
	
Returns:
	A decimal between 0 and 1 representing the calculation:
  [current month value] / [value from offset months ago] - 1
	
More details here:
https://www.flexyourdata.com/blog/excel-lambda-growthfromoffset-calculate-growth-of-current-month-over-12-months-before/
  
*/

=LAMBDA(month_col,value_col,month_offset,[if_error],
  IFERROR(
    LET(
      current_row,ROW()-MIN(ROW(month_col))+1,
      this_month,INDEX(month_col,current_row),
      this_value,INDEX(value_col,current_row),
      compare_month,EDATE(this_month,-1*month_offset),
      compare_value,SUMIF(month_col,compare_month,value_col),
      this_value/compare_value-1
    ),
    IF(ISOMITTED(if_error),NA(),if_error)
  )
)