To calculate every 12 weekdays (Monday to Friday) in a spreadsheet, a specific formula is not available, but it can be achieved through a combination of functions and manual adjustments. The WORKDAY function in Excel is useful as it calculates a date after a specified number of workdays, while also allowing for holidays. To find the 12th weekday after a given date, you can add 16 days (2 days plus 2 weeks) and adjust for additional days if the date falls on a Thursday or Friday. For adding the names of each day, you can input a starting date in one column and use a formula in the adjacent column to add 12 days, ensuring that Excel recognizes the date format. This method allows for easy replication by copying the formula down the column.