If the holder of an American-style option decides to exercise his right to buy (in the case of a call) or to sell (in the case of a put) the underlying shares of stock, the holder must direct his brokerage firm to submit an exercise notice to OCC. In order to ensure that an option is exercised on a particular day other than expiration, the holder must send any exercise instruction on that day.
Once OCC has been notified that an option holder wishes to exercise an option, it will assign the exercise notice to a clearing member - for an investor, this is generally his brokerage firm - with a customer who has written (and not covered) an option contract with the same terms. OCC will choose the firm to notify at random from the total pool of such firms. When an exercise is assigned to a firm, the firm must then assign one of its customers who has written (and not covered) that particular option. Assignment to a customer will be made either randomly or on a "first in first out" basis, depending on the method used by that firm. You can find out from your brokerage firm which method it uses for assignments.
The holder of a long American-style option contract can exercise the option at any time until the option expires. It follows that an option writer may be assigned an exercise notice on a short option position at any time until that option expires. If an option writer is short an option that expires in-the-money, assignment on that contract should be expected, call or put. In fact, some option writers are assigned on such short contracts when they expire exactly at-the-money. This occurrence is usually not predictable.
To avoid assignment on a written option contract on a given day, the position must be closed out before that day's market close. Once assignment has been received, an investor has absolutely no alternative but to fulfill his obligations from the assignment per the terms of the contract. An option writer cannot designate a day when assignments are preferable. There is generally no exercise or assignment activity on options that expire out-of-the-money. Owners generally let them expire with no value.
When an investor exercises a call option, the net price paid for the underlying stock on a per share basis will be the sum of the call's strike price plus the premium paid for the call. Likewise, when an investor who has written a call contract is assigned an exercise notice on that call, the net price received on per share basis will be the sum of the call's strike price plus the premium received from the call's initial sale.
When an investor exercises a put option, the net price received for the underlying stock on per share basis will be the sum of the put's strike price less the premium paid for the put. Likewise, when an investor who has written a put contract is assigned an exercise notice on that put, the net price paid for the underlying stock on per share basis will be the sum of the put's strike price less the premium received from the put's initial sale.
For call contracts, owners might make an early exercise in order to take possession of the underlying stock in order to receive a dividend. Check with your brokerage firm on the advisability of such an early call exercise. It is therefore extremely important to realize that assignment of exercise notices can occur early - days or weeks in advance of expiration day. As expiration nears, with a call considerably in-the-money and a sizeable dividend payment approaching, this can be expected. Call writers should be aware of dividend dates, and the possibility of an early assignment.
When puts become deep in-the-money, most professional option traders will exercise them before expiration. Therefore, investors with short positions in deep in-the-money puts should be prepared for the possibility of early assignment on these contracts.
Volatility is the tendency of the underlying security's market price to fluctuate either up or down. It reflects a price change's magnitude; it does not imply a bias toward price movement in one direction or the other. Thus, it is a major factor in determining an option's premium. The higher the volatility of the underlying stock, the higher the premium because there is a greater possibility that the option will move in-the-money. Generally, as the volatility of an underlying stock increases, the premiums of both calls and puts overlying that stock increase, and vice versa.