Calculate formula in text box, then give the result.

you cannot calculate with a textbox but you can refer to a (hidden) cell that holds the outcome of the required calculation

In your File I have put a sum formula under the data and refer to that cell in the textbox.

to put a cell-result in a textbox you need to have the formula bar visible in excel and then select the textbox then make a =$A$5 cell reference to show the result of that cell
the textbox will update every time the calculation changes

It works. Thank you