Start with the eligible item price
Verify that the coupon applies to the exact model, seller, quantity and fulfillment method. A category banner is not proof that every item qualifies.
Separate automatic and conditional savings
Automatic discounts are broadly reproducible. Account-targeted offers, first-order codes and membership benefits require clear labels because many shoppers will not qualify.
Add unavoidable costs
Shipping, required membership fees and mandatory accessories belong in the effective price. Optional add-ons do not.
Do not count rewards twice
Store credit and future rewards are not identical to cash off today. Their value depends on restrictions, expiration and whether the shopper would use them.