procedure TForm1.MicrosoftExcelDateFormatting(Sender: TObject);
var
   ExcelFileName: String;
   ExcelApplication, ExcelWorkbook, ExcelWorksheet: Variant;
begin
     //be sure ComObj and Variants units are included in the "uses" clause

     ExcelFileName := 'C:\PhysiologyWeb\delphi_code_examples\excel_file_date_formatting.xlsx'; //replace file name with the name of your file

     ExcelApplication := Null;
     ExcelWorkbook := Null;
     ExcelWorksheet := Null;

     try
        //create Excel OLE
        ExcelApplication := CreateOleObject('Excel.Application');
     except
           ExcelApplication := Null;
           //add error/exception handling code as desired
     end;

     If VarIsNull(ExcelApplication) = False then
        begin
             try
                ExcelApplication.Visible := True; //set to False if you do not want to see the activity in the background
                ExcelApplication.DisplayAlerts := False; //ensures message dialogs do not interrupt the flow of your automation process. May be helpful to set to True during testing and debugging.

                //Open Excel Workbook
                try
                   ExcelWorkbook := ExcelApplication.WorkBooks.Add(-4167);
                   //reference
                   //https://docs.microsoft.com/en-us/office/vba/api/excel.workbooks.add
                   //https://docs.microsoft.com/en-us/office/vba/api/excel.xlsheettype
                except
                      ExcelWorkbook := Null;
                      //add error/exception handling code as desired
                end;

                If VarIsNull(ExcelWorkbook) = False then
                   begin
                        //connect to Excel Worksheet using either the ExcelApplication or ExcelWorkbook handle
                        try
                           ExcelWorksheet := ExcelWorkbook.WorkSheets[1]; //[1] specifies the first worksheet
                           //reference
                           //https://docs.microsoft.com/en-us/office/vba/api/Excel.Worksheets.Item
                        except
                              ExcelWorksheet := Null;
                              //add error/exception handling code as desired
                        end;

                        If VarIsNull(ExcelWorksheet) = False then
                           begin
                                ExcelWorksheet.Select;

                                //add text to A1 cell [row,column]
                                ExcelWorksheet.Cells[1,1] := 'Microsoft Excel - Cell Number Formatting - Date Formatting';
                                //change the font size in A1 cell
                                ExcelWorksheet.Cells[1,1].Font.Size := 20;
                                //make A1 cell font bold
                                ExcelWorksheet.Cells[1,1].Font.Bold := True;
                                //change font color to blue
                                ExcelWorksheet.Cells[1,1].Font.Color := clBlue;
                                //change background color of A1 cell
                                ExcelWorksheet.Cells[1,1].Interior.Color := clYellow;

                                //add text to A3 cell [row,column]
                                ExcelWorksheet.Cells[3,1] := 'Hold your mouse over cells with numbers to see comments.';

                                //add text to A5 cell [row,column]
                                ExcelWorksheet.Cells[5,1] := 'Date Format';
                                ExcelWorksheet.Cells[5,1].Font.Bold := True;
                                ExcelWorksheet.Cells[5,1].Interior.Color := clAqua;

                                //add text to B5 cell [row,column]
                                ExcelWorksheet.Cells[5,2] := 'Format Code';
                                ExcelWorksheet.Cells[5,2].Font.Bold := True;
                                ExcelWorksheet.Cells[5,2].Interior.Color := clAqua;

                                //add text to C5 cell [row,column]
                                ExcelWorksheet.Cells[5,3] := 'Format Description';
                                ExcelWorksheet.Cells[5,3].Font.Bold := True;
                                ExcelWorksheet.Cells[5,3].Interior.Color := clAqua;

                                //add date, code, and description to row 6 [row,column]
                                ExcelWorksheet.Cells[6,1] := '=today()'; //adds today's date to A6 cell
                                ExcelWorksheet.Cells[6,1].AddComment('Default date format');
                                ExcelWorksheet.Cells[6,3] := 'Default date format';

                                //add date, code, and description to row 7 [row,column]
                                ExcelWorksheet.Cells[7,1] := '=today()';
                                ExcelWorksheet.Cells[7,1].NumberFormat := 'yyyy-m-d';
                                ExcelWorksheet.Cells[7,1].AddComment('Date format: year-month-day. 1 or 2 digits for month and day.');
                                ExcelWorksheet.Cells[7,2] := 'yyyy-m-d';
                                ExcelWorksheet.Cells[7,3] := 'Date format: year-month-day. 1 or 2 digits for month and day.';

                                //add date, code, and description to row 8 [row,column]
                                ExcelWorksheet.Cells[8,1] := '=today()';
                                ExcelWorksheet.Cells[8,1].NumberFormat := 'yyyy-mm-dd';
                                ExcelWorksheet.Cells[8,1].AddComment('Date format: year-month-day. 2 digits for month and day.');
                                ExcelWorksheet.Cells[8,2] := 'yyyy-mm-dd';
                                ExcelWorksheet.Cells[8,3] := 'Date format: year-month-day. 2 digits for month and day.';

                                //add date, code, and description to row 9 [row,column]
                                ExcelWorksheet.Cells[9,1] := '=today()';
                                ExcelWorksheet.Cells[9,1].NumberFormat := 'm/d/yy';
                                ExcelWorksheet.Cells[9,1].AddComment('Date format: month/day/year. 1 or 2 digits for month and day. 2 digits for year.');
                                ExcelWorksheet.Cells[9,2] := 'm/d/yy';
                                ExcelWorksheet.Cells[9,3] := 'Date format: month/day/year. 1 or 2 digits for month and day. 2 digits for year.';

                                //add date, code, and description to row 10 [row,column]
                                ExcelWorksheet.Cells[10,1] := '=today()';
                                ExcelWorksheet.Cells[10,1].NumberFormat := 'mmmm d, yyyy';
                                ExcelWorksheet.Cells[10,1].AddComment('Date format: month day, year. Full month name.');
                                ExcelWorksheet.Cells[10,2] := 'mmmm d, yyyy';
                                ExcelWorksheet.Cells[10,3] := 'Date format: month day, year. Full month name.';

                                //add date, code, and description to row 11 [row,column]
                                ExcelWorksheet.Cells[11,1] := '=today()';
                                ExcelWorksheet.Cells[11,1].NumberFormat := 'mmm d, yyyy';
                                ExcelWorksheet.Cells[11,1].AddComment('Date format: month day, year. Short month name.');
                                ExcelWorksheet.Cells[11,2] := 'mmm d, yyyy';
                                ExcelWorksheet.Cells[11,3] := 'Date format: month day, year. Short month name.';

                                //add date, code, and description to row 12 [row,column]
                                ExcelWorksheet.Cells[12,1] := '=today()';
                                ExcelWorksheet.Cells[12,1].NumberFormat := 'dddd, mmmm d, yyyy';
                                ExcelWorksheet.Cells[12,1].AddComment('Date format: weekday, month day, year. Full name for weekday and month.');
                                ExcelWorksheet.Cells[12,2] := 'dddd, mmmm d, yyyy';
                                ExcelWorksheet.Cells[12,3] := 'Date format: weekday, month day, year. Full name for weekday and month.';

                                //add date, code, and description to row 13 [row,column]
                                ExcelWorksheet.Cells[13,1] := '=today()';
                                ExcelWorksheet.Cells[13,1].NumberFormat := 'ddd, mmm d, yyyy';
                                ExcelWorksheet.Cells[13,1].AddComment('Date format: weekday, month day, year. Short name for weekday and month.');
                                ExcelWorksheet.Cells[13,2] := 'ddd, mmm d, yyyy';
                                ExcelWorksheet.Cells[13,3] := 'Date format: weekday, month day, year. Short name for weekday and month.';

                                //add date, code, and description to row 14 [row,column]
                                ExcelWorksheet.Cells[14,1] := '=today()';
                                ExcelWorksheet.Cells[14,1].NumberFormat := 'mmmm yyyy';
                                ExcelWorksheet.Cells[14,1].AddComment('Date format: month year. Full name for month.');
                                ExcelWorksheet.Cells[14,2] := 'mmmm yyyy';
                                ExcelWorksheet.Cells[14,3] := 'Date format: month year. Full name for month.';

                                //add date, code, and description to row 15 [row,column]
                                ExcelWorksheet.Cells[15,1] := '=today()';
                                ExcelWorksheet.Cells[15,1].NumberFormat := '[$-00000000]dddd, mmmm d, yyyy';
                                ExcelWorksheet.Cells[15,1].AddComment('Date format: weekday, month day, year. Default system settings for date/time.');
                                ExcelWorksheet.Cells[15,2] := '[$-00000000]dddd, mmmm d, yyyy';
                                ExcelWorksheet.Cells[15,3] := 'Date format: weekday, month day, year. Default system settings for date/time.';

                                //add date, code, and description to row 16 [row,column]
                                ExcelWorksheet.Cells[16,1] := '=today()';
                                ExcelWorksheet.Cells[16,1].NumberFormat := '[$-en-US]dddd, mmmm d, yyyy;@';
                                ExcelWorksheet.Cells[16,1].AddComment('Date format: weekday, month day, year. English - United States locale.');
                                ExcelWorksheet.Cells[16,2] := '[$-en-US]dddd, mmmm d, yyyy;@';
                                ExcelWorksheet.Cells[16,3] := 'Date format: weekday, month day, year. English - United States locale.';

                                //references
                                //https://learn.microsoft.com/en-us/office/vba/api/excel.cellformat.numberformat
                                //https://learn.microsoft.com/en-us/dotnet/api/documentformat.openxml.spreadsheet.numberingformat

                                //autofit the width of Column A
                                ExcelWorksheet.Columns[1].EntireColumn.AutoFit; //autofits Column A
                                ExcelWorksheet.Columns[2].EntireColumn.AutoFit; //autofits Column A
                                ExcelWorksheet.Columns[3].EntireColumn.AutoFit; //autofits Column A
                                //reference
                                //https://docs.microsoft.com/en-us/office/vba/api/excel.range.autofit

                                //select A1 cell
                                ExcelWorksheet.Cells[1,1].Select; //selects Cell A1

                                ExcelWorkbook.SaveAs(ExcelFileName);
                                //Note: If a file with the new name already exists, it overwrites it. Write additional code to address as desired.
                                //reference
                                //https://docs.microsoft.com/en-us/office/vba/api/excel.workbook.saveas
                           end;
                   end;
             finally
                    ExcelApplication.Workbooks.Close;
                    ExcelApplication.DisplayAlerts := True;
                    ExcelApplication.Quit;

                    ExcelWorksheet := Unassigned;
                    ExcelWorkbook := Unassigned;
                    ExcelApplication := Unassigned;
             end;
        end;
end;