How many shares of a Stock should you buy when Day Trading? It really comes down to your maximum loss! Gauging the particular stock that your trading and assessing closest support/resistance if the trade does go against you where will you have to take a loss. Whenever I’m sizing into trades I’m making a plan of where Ill look to cut my loss and how many shares I can take to achieve that. Being consistent with your sizing while DayTrading is key to being consistently Profitable.