A family of Microsoft spreadsheet software with tools for analyzing, charting, and communicating data.
You can set the linked cell of the check boxes to the cell they occupy, i.e. set the linked cell if the first check box to A1, etc.
The cell will then contain TRUE or FALSE depending on the state of the check box.
The formula to return the percentage of ticked check boxes in A1:D1 is
=COUNTIF(A1:D1, TRUE)/COUNTA(A1:D1)
Format the cell with the formula as a percentage.