It is rather simple to calculate the food cost percentage. The formula is: portion cost divided by the menu/food cost multiplied by 100 percent. For example: It costs $3.00 to produce the food and you buy it for $6.00. Take $3.00/$6.00 = .5. Now take .5 multiplied by 100 percent and you get 50 percent. Food Cost Percentage www.members.shaw.caReference: www.members.shaw.ca1 Additional Answer You would calculate the food cost percentage by the net sale. If you were to cater a get together and charged $1000 and the food used for preparation came to $370, you would take 370 divided by 1000 which would be 37%.