For the most part, the only real restriction is that you have to have cash on hand to settle any purchases that day regardless of any sales. The next day all the transactions settle and you can continue. So you just have to keep a larger cash reserve if you’re going to do a lot of swing trading.

Some brokers are more flexible with that and will cover you as long as your trades don’t put your cash in the negative, but that’s up to the broker to manage the risk of a failed transaction.

Or so I understand it.