Two stacked discounts never add up cleanly. A 20% + 10% combo only saves 28%, not 30%, because the second percent applies to the already-reduced price.

The ‘best of’ mode picks whichever single discount saves more — useful when a store's terms say ‘not combinable with other offers.’

BOGO offers convert cleanly to a per-unit price: ‘Buy 2 get 1 free’ at $30 each = $20 effective. The calculator shows the true per-unit cost so you can compare against a straight % off.