Unless you lose those gains on other plays before December 31st you WILL pay tax and the 40% or 20% ppl throw around is NOT accurate as it's a percentage based on bracket and for long term CAN be as low as 0% if u fall in a certain EARNED income tax bracket......
Oh and your tax bracket is NOT determined by your gains it's by your EARNED income.
Just make sure if you make big gains to get a good accountant and don't base holding long term vs short term on gains taxes as taxes all have built in LOOPHOLES