To get a list of customers categorized by birth date, run a Customer Report:
1. Go to Marketing>Reports>Customers
2. Click on the download as Excel button
3. Open the Excel spreadsheet
4. Create an extra column called "Birthday", and paste this formula
=TEXT(A1, "mm") & "/" & TEXT(A1, "dd")
You will have to replace A in the formula with the Excel column letter(s) where the birthday custom field shows. In the example below, the A should be replaced with L, as the Date of birth shows in Column L.
You can simply expand the formula to all rows with the mouse, and you have the birthday of all your customers.
5. You can now sort customers by birth date.