Zero! Bitcoin Gambling sites do not take any commission from your deposits or withdrawals. You can simply transfer your desired deposit amount to the betting site without the betting site taking any commission out of it. It is the same with withdrawals. You will get exactly whatever the requested withdrawal amount is. You might need to pay commission to your Bitcoin wallet when you make the deposit transfer so be careful to choose a low commission crypto wallet. If you do not want to use a crypto wallet you can directly buy crypto money from the Bitcoin betting and gambling sites such as Sportsbet.io, Bitcasino and 1xBit.