Work out buy one get one value instantly with clear inputs, formula shown and shareable results.
A BOGOF is only a 50% discount if you use both items. Divide the total cost by the units you will actually consume, not the units you receive, and offers on perishables often turn out to be no saving at all.
Multi-buy value
effective price = total paid / units actually used; headline discount = 1 - paid units / units received
3 for 2 is a 33% discount, BOGOF is 50%. Both require you to want the extra units for the discount to be real.
Wasting the free item converts a 50% discount into no discount at all, and you have also spent more cash up front.