[QUESTION- HELP NEEDED] I can't set a date as the column header in a table?

Hello - I am working on a table of data in an Excel spreadsheet, I am having some difficulty with the table headers as I am not able to set these as formulas or dates. Once I convert the data into a table, the headers convert to text. What am I doing wrong? I really need to have dates, which are formula-driven as the column headers. I hope someone here can help?