I have a column of data formatted as ‘date’ currently in dd/mm/yyyy . if I change to format to yyyy-mm-dd using the Format Cells option, the date stays as dd/mm/yyyy.

This was a csv file import a I reformatted the column from ‘general’ to ‘date’ and each cell is showing as ‘Date’ type so I cannot put my finger on what I am doing wrong.



This means that you have imported the column values as text (e.g., because your data didn’t fit into chosen locale’s date format, or you haven’t used Detect special numbers feature). So now those "dd/mm/yyyy"s are simply strings, and cell formatting doesn’t mean anything there.

You need to convert the data to dates first. To do that, use Data→`Text to Columns…" and select proper date format for the column (right-click on the column header in the dialog).

Perfect, all working now, thank you very much.