I have a spreadsheet that has total hours for Jan, Feb, Mar, Apr, May, Jun,
Jul, Aug, Sep, Oct, Nov, Dec. (B21:M21) In these fields are values up until
the current month.

I have a field called Total Hours (B7). How can I get this cell to
reference the current month? Can it be done?

So for this month I keyed 144 in the month of Aug and I want the field Total
Hours to reflect that total automatically. For next month, it should change
to the figure keyedin Sep.