WORKDAY Function in Excel

The calculated date falls outside valid Excel date range (before 1/1/1900 or after 12/31/9999), or start_date is not a valid date value. This commonly occurs when using negative days that go too far back, or when start_date cell is empty or contains text.

1. Verify start_date contains a valid date (check cell format) 2. Ensure days value doesn't create date before 1/1/1900 3. Check that start_date isn't empty or text 4. Use IFERROR to handle invalid inputs: =IFERROR(WORKDAY(A2,10,Holidays),"Invalid Date") 5. Add data validation to prevent invalid date entries

Always validate input dates before calculation. Use data validation rules on date cells to ensure valid entries. Consider adding IF statements to check for blank cells: =IF(ISBLANK(A2),"",WORKDAY(A2,10,Holidays))

One or more arguments are invalid data types. Most commonly caused by: text strings that Excel cannot interpret as dates in the holidays range, non-numeric values in the days argument, or dates formatted as text in the start_date parameter. Also occurs when holidays range contains mixed data types (dates and text).

1. Check holidays range for text entries - all must be valid dates 2. Ensure days parameter is numeric (not text) 3. Convert text dates using DATEVALUE: =WORKDAY(DATEVALUE(A2), 10) 4. Verify start_date is not formatted as text - check with ISTEXT(A2) 5. Clean holidays range: remove blank cells, text, non-date values 6. Use date functions instead of text: DATE(2024,1,15) instead of "1/15/2024"

Format all date cells with Date format (not General or Text). Use Data Validation to restrict input to dates only. Create holiday lists using DATE() function or consistent date entry format. Use named ranges with clear data types.

Most commonly caused by: 1) Forgetting that WORKDAY excludes the start date in counting (counts FROM start, not INCLUDING start), 2) Holidays range has incorrect date formats or missing holidays, 3) Time component in start_date causing date serial number issues, 4) Regional date format mismatches (MM/DD/YYYY vs DD/MM/YYYY), 5) Expecting calendar days but WORKDAY counts business days only.

1. Understand WORKDAY counts FROM start_date, not including it - if project starts Monday and takes 5 days, it completes on following Monday (not Friday) 2. Verify all holidays are in the holidays range - missing holidays shift results 3. Remove time components: use INT(A2) or DATE(YEAR(A2),MONTH(A2),DAY(A2)) 4. Check regional settings match date format 5. Test with known date scenarios: =WORKDAY(DATE(2024,1,15),5) should equal 1/22/2024 (Monday to Monday) 6. Compare with NETWORKDAYS to verify business day count: =NETWORKDAYS(start,WORKDAY(start,days,holidays),holidays) should equal days

Always use consistent date formats. Document whether start date is included in count. Test formulas with simple scenarios before complex implementations. Use DATE() function for unambiguous date creation. Maintain comprehensive holiday lists updated annually.