Sorry, I'm sometimes a bit of a dunce.

I have 39438 rows where column M will only have number 1 to 12 to show during which month a sale was made. I don't think selecting the column first works, I can only seem to do that by sheet or workbook (although it would made sense to have a 'selected cells only' option).

I'm pretty sure nawas or martindwilson are on the right track, but where do I put these formulas?