- Suppose you bought a 100 shares of a stock at $40 a share and the initial margin requirement is 70%. Therefore, you will borrow 0.30$4,000, or $1,200. The remaining $2,800 needed to buy the securities represents your equity in the transaction. - If the stock price drops to $15 a share, then how much additional equity you need to put into your account (assuming you need to pull the margin level to the initial margin)