Basic long/short margin question

Let's say you have a $10,000 portfolio. You want to buy stock A which trades at$100 and short stock B which also trades at $100, at 150%/50% respectively. So you buy 150 shares of A and sell 50 shares of B. Let's assume for the moment that maintenance margin requirements are 30% on both stocks. So right now your maintenance requirement is$6,000 (right?)

Can somebody help me understand what happens to your maintenance margin requirements if both stocks A and B fall in price by $X? Say they both fall from$100 to $50. 4 responses Eii! Margin calculations are annoying. I can't attach a spreadsheet here, but in your above example, I believe the value of your position in A drops from$15k to $7.5k and your loan on position B drops from$-5k to $-2.5k, so your overall portfolio equity drops from$10k to $5k, while your margin requirement drops from$6k to $3k.$5k > $3k so you still don't get a margin call. I think I have that right. IB has some examples here: https://gdcdyn.interactivebrokers.com/en/index.php?f=marginnew&p=overview3 See, that's what I thought too (based entirely on IB's margin examples), but then I tried seeing what would happen if both stocks dropped by 90%, and it somehow appeared I still wasn't getting a margin call (which seems weird - you'd think they'd want their money back before that point). Well, if the long goes down and the short goes up, you'll quite quickly get a margin call... Or, if you use more margin. A 30% margin means you could have more notional than that, on a$10k equity base, and then that would also quite quickly flame out...