Why does coffee GENERALLY have 0 calories (plain, black), but then Dunkin Donuts coffee is either 15 or 30?

Question

Why does coffee GENERALLY have 0 calories (plain, black), but then Dunkin Donuts coffee is either 15 or 30 calories? (Also, is coffee REALLY zero calories even if you drank, hypothetically, a whole gallon?)

Answer 1

Plain black coffee contains nothing but water and coffee beans. The calorie content in coffee beans is negligable.

Most of the calories would come from the added sugar, whitening, milk and flavors that are added into the coffee.

Answer 2

Added flavoring?  Coffee may not be fattening, but like baked potatoes, it's all the stuff you add to it....sugar, milk, cream, sugar syrups.