An investor can increase his/her account buying power by using borrowed money, or leverage. Those who trade on U.S. stock market are allowed to use up to 4:1 leverage. It means your buying power is 4 times bigger than your account balance. If you have $25,000 on your account, you can accumulate positions up to $100,000. Traders who hold their positions overnight (that is they do not sell them before the market closes) are allowed to use up to 2:1 leverage. If you exceed this ration (for example, you lose some position and your account balance drops).