I believe that they allow 3.3x initial leverage and require 15% maintenance margin in order to maintain positions. By my calculations, this means that there would need to be a very swift change in price in excess of 10% for the possibility of individual accounts to have negative equity.
Users do not have to use the maximum amount of leverage (although lenders do not have any control over this).
I would point out that, according to
https://www.bfxdata.com/positions/btcusd as of Jan 6 at 8:59, the price of BTC was 1,151.16, and there were 37,349
BTC in outstanding BTCUSD long positions, and as of Jan 6 at 17:59, the price of BTC was 962.26 (down ~16.4%), and there were 26,422
BTC in outstanding BTCUSD long positions (down ~10,900
BTC, or ~29.25%). This did of course follow a very sharp upward movement in the BTCUSD price, and is only one example of how the market on Bitfinex specifically handled one specific quick selloff.
I don't quite understand what you mean to say
But maybe it's just me, after all. Regarding the amount of leverage, 3.3:1 leverage means that the trader can potentially have 3.3 times the amount that he actually has. In this manner, if he has, say, only 100 dollars he could buy bitcoins for the total of 330 dollars (including his own money). If the price goes higher, that would give him 3.3 times more profit, but if the price goes down dramatically he could potentially incur more losses than he has funds in his account. With 3.3:1 leverage that would happen if the price went down 33%, but since the exchange has the right to forcefully sell his bitcoins (to prevent them from losses), they will do that even before the price comes down to the point where the account will get wiped away completely
If someone has $1,000 in USD, they can buy 3.3
BTC @$1,000 each (ignoring trading fees, and interest payments). This person will owe $3,300 to lenders. If the price of
BTC declines to $850, then the 3.3
BTC that he purchased is now worth $2,805, he will still have his initial $1,000 and will have total assets of $3,805; he will still owe $3,300 to lenders, so his net equity is $505, or 15.3% of what he owes to lenders. He would get a margin call at roughly this time.
If the price were to fall to $697 (18% decline from $850), then the value of that 3.3
BTC would be $2,300.1, plus his initial $1,000 would mean that his total assets are $3,300.1 and the amount lent to lenders would be $3,300, however after factoring in trading fees and interest, his assets would be less than the amount owed.
So it seems that the more precise statement is that the price will need to fall by roughly 18% from a point very quickly for there to be a risk that individual accounts having negative equity.
I would point out that it is theoretically possible for someone to buy 3.3
BTC in the above scenario, and for the price of
BTC to remain the same for a long enough period of time, and the interest payments cause a margin call.