Gross profit calculator If you would like to calculate your Gross Profit, and Gross Profit Margin, please enter the details of your sales below and press the Calculate button. Sales (£): The total value of sales made. Cost of sales (£): The total cost of all items sold. Calculate Note: These calculations are only for illustrative purposes and are not a substitute for professional advice. The NI calculation is annualised and therefore due to the change in the employee rate during the year, the amount is only an indication.