The frustratingly vague answer to this commonly asked question is: it depends. In America at least, every state makes its own laws regarding these sorts of things, but at the end of the day we can tell you that straight up, clean card counting is certainly not illegal anywhere in the USA… but that doesn’t mean you’re not going to get kicked out of the casino!
Why would anyone get thrown out on the Las Vegas strip if card counting’s not illegal? Basically because casinos don’t like it, and the second you whip out a notepad or an iPhone with a card counting app on it, you’ll be asked to leave. The official reason for this is that you may be cheating or compromising the casino’s security by doing these underhanded (or blindingly obvious) little things. In Nevada, it’s illegal to go to the casino with anything that will help you gain an advantage against the house, and that might include anything from a smartphone to loaded dice! Apparently the casino gift shops themselves sell ‘strategy cards’ which basically give you tips and hints on how to win, but that certainly isn’t equal to using a card counting app on your phone! The general consensus is that if you do the card counting purely in your head, you can get away with it until someone at security notices you winning and starts tracking your play – card counting calls for wild variations in betting size and that’s how they’ll catch you out and you’ll be asked to leave.