New Post: Problem with the formula

Replace the Semicolons ";" with commas "," to read like this:

worksheets.Cell(2, 2).FormulaA1 = "=IF(A6>$A$4,0,1-(E6+F6)/C6)"; 

I will typically test out the formula manually in Excel to see if it works first, and then use it with the same syntax with ClosedXML.