And to calculate your ROI, the formula is simple:
Total Profit / Investment*100 = ROI %
(Note that Total Profit = Total Winnings - Investment...do not skip this, ROI is based on Total Profit, not total winnings.)
So for a tournament with a buy-in of $11.00 and say you win $45. Your Total Profit = $45 - $11 = $34. Your ROI = $34/$11 = 3.0909 * 100 = 309.09%
Or, same calculation in a single formula is: (Winnings - Buyins) / Buy-ins * 100