based on the margin and credit balance data - NYSEData.com Factbook Chart courtesy of www.marketvolume.com Starting from 2013 we have increase in margin and decrease in the credit balance. As of the last available data (as of March of 2015), credit balance now is 29% of the margin on all trading accounts. According to the margin requirements rule #431 - "The margin which must be maintained in all accounts of customers, except for cash accounts subject to Regulation T unless a transaction in a cash account is subject to other provisions of this rule, shall be as follows: (1) 25% of the current market value of all securities except for securities futures contracts "long" in the account." If we have a market correction, let's say 7%, it will go as a loss for all trading accounts which are in "Long". Respectfully it will lower the credit balance, and if it the credit balance drops below 25% it will create margin calls which will add selling to the market which may lead the market to decline further with following chain reaction of the massive margin calls and selling? I would appreciate of an input whether I understand correctly the numbers.