Shorting Stocks And Margin Account Minimum
The margin money you put up to fund a short position ($6000 in the example given) is simply a "good faith" deposit that is required by the broker in order to show that you are acting in good faith and fully intend to meet any potential losses that may occur.  This margin is normally called initial margin.  It is not an accounting item, meaning it is not debited from you cash account.  Rather, the broker simply segregates these funds so that you may not use them to fund other trading.  When you settle your position these funds are released from segregation.   In addition, there is a second type of margin, called variation margin, which must be maintained while holding a short position.  The variation margin is simply the running profit or loss being incurred on the short position.  In you example, if you sold 200 shares at $20 and the price went to $21, then your variation margin would be a debit of $200, while if the price went to $19, the variation margin would be a credit of $200.   The variation margin will be netted with the initial margin to give the total margin requirement ($6000 in this example).  Margin requirements are computed at the close of business on each trading day.  If you are showing a loss of $200 on the variation margin, then you will be required to put up an additional $200 of margin money in order to maintain the $6000 margin requirement - ($6000 - $200 = $5800, so you must add $200 to maintain $6000).  If you are showing a profit of $200, then $200 will be released from segregation - ($6000 + $200 = $6200, so $200 will be release from segregation leaving $6000 as required). When you settle your short position by buying back the shares, the margin monies will be release from segregation and the ledger postings to you cash account will be made according to whether you have made a profit or a loss.  So if you made a loss of $200 on the trade, then your account will be debited for $200 plus any applicable commissions.  If you made a profit of $200 on the trade then your account will be credited with $200 and debited with any applicable commissions.