margin call occurs when the value of an investor's margin account (that is, one that contains securities bought with borrowed money) falls below the broker's required amount. The investor must either deposit more money in the account or sell some of the assets held in the account.Calculate the amount of money per share borrowed from your broker for your margin trade. To do this, subtract the margin requirement from 1 and multiply by the market (purchase) price. Suppose you buy stock at $40 per share with a 60 percent margin requirement.margin call occurs if your account falls below the maintenance margin amount. ... You are responsible for any losses sustained during this process, and your brokerage firm may liquidate enough shares or contracts to exceed the initial margin requirement