How do I calculate customer loyalty discounts on orders?

Your question seems ambiguous, and I can draw two conclusions about what you're trying to achieve here:

1. Calculating The Cost of Customer Loyalty Program: To calculate your per-unit loyalty program cost, you need to divide the cost of rewards ordered by the total loyalty currency spent.
2. Measuring Customer Loyalty Performance: Determine your customer retention rate to gauge the results brought in by the customer loyalty program. Customer retention rate is obtained by dividing the total number of repeat customers over a specific time by the number of total customers.

I hope this helps!