Was trying to work out how much a 10% tax on winnings will affect ROI. I tried thinking about it like this. Lets say there is a 1k tournament and we have 100% ROI and play it 100 times. So we pay 100k in buy ins and make 200k in prizes, giving us net profit of 100k and 100% ROI. If we then have to pay 10% tax on winnings, that means we only make 180k in prizes and a net profit of 80k, changing our ROI to 80%.

Is there any flaw in my maths? Or does a 10% tax really decrease your ROI by more than 10%