What is BOGO (buy one, get one)?
BOGO is a promotion in which a shopper who buys one item gets a second item free or at a discount. The second item is usually the same product, though it can be a different one.
The margin cost is easy to underestimate: a full BOGO on a product with a 60 percent margin gives away the whole unit cost of the second item, and any shoppers who would have bought one unit anyway now cost you a free unit.
BOGO is a special case of buy X get Y with X and Y both set to one.