It would help if you told us what software you are working with.
If you are using some version of Microsoft Excel, you should format columns A and B to use your desired date format. Subtracting their values will return the number of days. Using Excel's VLOOKUP function is probably the easiest way to convert the number of days to the desired group description.
I have attached an example MS-Excel file.
If you are using some version of Microsoft Excel, you should format columns A and B to use your desired date format. Subtracting their values will return the number of days. Using Excel's VLOOKUP function is probably the easiest way to convert the number of days to the desired group description.
I have attached an example MS-Excel file.