What the GP result includes
Hospitality till prices normally include VAT. Gross profit should compare the sale after output VAT with the recoverable cost before input VAT. If your invoice figure includes VAT, select that option so the calculator removes it.
What GP does not include
This is product gross profit, not net profit. Labour, rent, card fees, utilities and other overheads remain outside the calculation unless they are deliberately added to the product cost.
Pricing draught? A simple unit cost misses ullage, line cleaning and short measures. Use the draught yield calculator instead.