How can i count the amount of taxes i have to pay after i won?

Only gambling profits are taxed in casinos. This means that even if you win big, you can deduct your losses as long as you keep some evidence such as tickets. In all cases though, you cannot claim losses that are more than your winnings. You can ask the casino for a win/loss statement to help you determine how much money you’ve won and how much of it is taxable.
 
The only games in casinos that get taxed are bingo, keno, and slot machines. All table games, including blackjack, craps, poker, and roulette do not get taxed as the casinos have no way of figuring out how much money you started with. The IRS does not require reports of any wins in these table games.