How to calculate New customers and Returning customers in a Pivot Table?

Hi,

I have a Pivot table with columns as Order Date, Customer Name, Qty, Cost, Freight, Invoice, Adv Payment. I have only 30 customers and 11000 transactions for 4 years sales period.

How to calculate New customers and Returning customers in Pivot Table for any given Month or Quarter or Year. I am open to use helper column, formula or a calculated field etc

Thanks
Arjun