Let me put a finer point on it and use hard numbers, because I think the crux of what I'm trying to get to the bottom of is this: are brokerages required by law to monitor (and have risk controls to prevent) real-time
assignment liability,
even when a spread -- at the time it's opened -- would be fully hedged?
Example:
You have a $16K cash balance on
June 20th and AMZN's trading at
$2,615. Being neutral-to-bullish, you put on this spread:
i) Buy 3 x
July 17th $2,610 Puts for $26.00 each (tot cost: $7,800)
ii) Sell 3 x
July 17th $2,615 Puts for $28.00 (tot premiums received: $8,400)
Your account balances are now:
a) Long 3 x 2,610 Puts
b) Short 3 x $2,615 Puts
c) $16,600 cash
No disagreement (i hope) that
at the time you put on this trade:
i) You're +$600 from the difference in the premiums paid/received;
ii) Your max loss is -$900 (if both legs expire ITM > -$1,500 + $600 premiums)
So as some ITT have pointed out, there's little risk here in letting a $16,000-value account put on this spread when his max loss is $900.
However there's absolutely much higher risk that can accrue as Expiry approaches. If at 3:55pm on July 17th AMZN's underlying is trading at
$2,613, and it looks like his Long
$2,610 will expire OTM but he'll be Assigned on the
$2,615 short, a client (and his brokerage) would be looking at significant liability over the weekend. E.g. if there's bad news for AMZN and it opens Monday at $2,400, the client's account balances would be:
i) Long 300 AMZN (value: 300 x $2,400 = $720K)
ii) (-$767.9K) negative cash balance ($16.6K from above -$784.5K from Assignment on $2,615 Put)
>> Even if a brokerage liquidates the 300 x AMZN near the open, the client is in ~$48K in the hole (3x the size of a $16K account!)
My questions are:
Do brokers have risk controls that would prevent a $16K account from putting on the above spread all the way back on June 20th, on the theory that even though there's little risk at the time, there
will be risk (or at least there
could be) that accrues closer to expiry? And if they do have such controls, is that required by law or just by individual brokerage policy?
(I
think the way IB handles this is that they calculate the expected post-expiry margin snapshot as Expiry approaches, and if you'd be in a margin deficit (assuming all ITM exercises), they liquidate positions
prior to Expiry; e.g. in the example above, they'd liquidate the short 3 x $2,615 Put / aka force client to close it with the account's $16,600 cash balance -- before the value of the short exceeds that, of course -- as Expiry approaches.)