Let's say I have $50K in my account. Also, I am long 100 contracts of a 95/100 bull call spread with the underlying at 105 at expiration. Obviously, both the long and short legs of the spread will be automatically exercised. However, my account balance or even my day trading buying power is not enough to cover the cost of buying 10,000 shares of the underlying at $95. My question is this: does my account balance matter here since the buy and sell will only be paper transactions and I should be credited with the $50K (5*100*100) after the calls are exercised? Or will the broker loan me the amount to buy the underlying at $95 (even though my $50K is not enough margin for such a huge loan) and then charge me interest on nearly $900K? Thanks.