Here is my thought,
start with list of customers and get minimum date for which they purchased first. This way you will get List of customers with their start in the system. Now with same data reversed. You need to plot all those min(dates) with distinct count(customers)
This will give you unique customers which got added freshly in the system.
Please find the attached workbook for your reference.
Retention.twbx 50.3 KB
Hi Amit, Thank you for your help! the logic you suggested worked on my dashboard. Vandana