I underpaid my taxes last year and now I'm paying estimated taxes for this year. This sucks, obviously, but I starting thinking...if you are a trader and make money, do you get reamed for not pre-paying your taxes? How does this work? I just started trading this year and never thought about this until now. If I made, say $100k this year, I could end up having to pay a shitload of pre-paid taxes next year by IRS rules. Now that would really suck.