Nope. No idea on actual rules.
Working out expense and income sources would be a good start though. If you could work out approximate values for each, you would get an average profit/loss.
Once off (or rarely recurring) expenses:
Purchase of land/building (if not leasing)
Furnishings/Refurbishment
Brewing Equipment
Initial stocks of food/drink
Cash float
Regular Expenses
Brewing ingredients
Other beverages not produced on site
Food
Firewood
Staff (cook x 2, serving wench x 2, manager, odd-job boy??, stable-hand)
Repairs after revelry
Entertainment
Advertising
Rental (if property not owned)
Taxes (including licencing if necessary)
Income Sources
Drinks
Food
Stabling
Lodging
How many patrons are you expecting? Do you have competition? Are you offering stabling? What drinks are you brewing on site?
(Cost per drink - cost to purchase - tax paid) x expected sales = cash income per night from drinks.
Keep in mind that medieval beer and many other drinks did not "keep" and had to be brewed and brought in fresh on a regular basis.