He sold those calls 4 months ago before AAPL tanked. So, I would assume AAPL was was trading right around $330.00.
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Here is your real short answer:
If he did not cover those short calls when the had a beautiful chance to do so he would be sitting on an $18,382.00 loss today.
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I assume he sold these calls naked. To set that trade up, he would have to meet margin requirements. Margin on short options used to be 35% of the value of the stock, plus or minus any amount in or out of the money the options are from their strike price and less the premium sold.
For one contract: stock is $320 x 35% = 112. The 335 call is $15.00 out of the money = $112.00 - $15.00 = $97.00 less the $13.86 premium.
$97.00 - 13.86 = $83.14. One contract is for 100 shares of stock. So, $83.14 x 100 = $8314.00
So, to short one OTM 335 call, the seller has to be able to cover $8314.00. Since he says he sold 13 contracts, he has to cover $8314.00 x 13 = $108,082 to set that trade up.
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Right after he sold that contract, AAPL tanked down to $220.00. He was golden. With a 335 call now OTM by 115 points, there would not be very much time premium. If he covered at that time, and let's say he could have bought those calls back for $ 0.50. .50 x 100 = $50.00 x 13 = $650.00.
He would have netted $13.86 x 13 = 180.00 x 100 = $18018.00 - 650.00 = $17,368.00 on that trade.
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OK. Let's assume he was not paying attention to business and he did not buy back those short calls. Let's assume he is still short those 13 calls.
Here is your short answer: AAPL is now trading at $363.00.
He sold the 335s for a $13.86 premium.
$363.00 - 335 = $28.00 - 13.86 = $14.14
So, right now, he is losing ( $14.14) per share or. 14.14 x 100 = $1,414.00 x 13 = ($18,382.00).
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EDIT: If he is still short, he would be getting buried in margin calls because his calls are $28.00 ITM.
EDIT 2: It sounds complicated, but is really not. Once you have made a couple of options trades, the math starts falling right into place. It is amazing how fast you learn the math when you are getting hammered by a losing trade
The rub is no different than if you are trading stocks. You still have to have the understandings of what is making your stock move and the market move.
If you buy a simple call and pay $2.50 x 100 = $250.00 your max loss is $250.00. $250.00 is gambling bet. Put your bet on and watch the wheel spin. Maybe you get lucky. Maybe you don't.
But when you go on the short side of selling options naked, you really have to pay attention. $250.00 is a gambling bet. Although, unlike Vegas, you can pull your bet at any time if you don't like the way things are looking.
Going short can make you start chewing your finger nails down to the quick. It is so easy to get over-leveraged.