We use the same method of calculating recipe costs used by commercial foodservice operations - adding the costs of each ingredient used, in the amount used, rather than adding the full price of items purchased. Some argue that you can’t just buy 1 tbsp of peanut butter, so the recipe should actually cost more. Our answer to that is you wouldn't buy an entire jar of peanut butter every time you make a recipe, nor would we consider an ingredient free if we already had it in our pantry. Both methods have their pros and cons, but the method we use is the most accurate indicator of what you'll actually spend in a month.