The Gross Profit is the difference between the dish or menu selling price and the dish or menu cost price (income - expense).
To calculate the Gross Profit, the cost price is subtracted from the selling price (excl sales tax).
This amount as a percentage of the selling price (excl sales tax) gives you the GP%.
Example: If a dish is costed at 2.32 and sold at 8.95 (excl sales tax)
Subtract the dish cost price from the dish sell price to get the Gross Profit: 8.95 – 2.32 = 6.63
Calculate what the cost is as a percentage of the selling price to get the GP%: (6.63 / 8.95) * 100 = 74.07821%