What happens if my call option expires in the money?
In the US, an expiring stock option that is at least one cent in the money is normally exercised automatically by the clearing house unless you instruct otherwise. For a call, that means you pay the strike price for 100 shares and receive the shares. The call's worth is the difference between the shares' value and the cash you pay. If your account can't pay for the shares, your broker's own rules decide what happens, so read them before expiry day.
Try it: a call with a $50 strike, bought for its model price with 30 days left at 30% implied volatility (made-up numbers). Set where the stock closes on expiry day.
Simulated example, priced by the StrikePath engine (Black–Scholes, interest 4.3% a year). For learning; not advice.
The automatic exercise
The Options Clearing Corporation exercises an expiring stock option that is $0.01 or more in the money unless the account holder or broker instructs otherwise; the threshold was lowered to one cent in 2008 (SEC Release No. 34-57163, 16 January 2008, the order approving OCC's change to its expiration-date exercise procedure). Brokers add their own deadlines and rules, so the place to check is your broker's options agreement.
Selling before the close instead
Many option buyers sell an in-the-money option before it expires rather than take the shares. Close to expiry its price is close to what exercising is worth, less half the bid-ask spread. Selling avoids needing the cash for 100 shares and the risk of holding them over a weekend; exercising avoids the spread. Which suits you is your call; the demonstration on exercise or sell shows the trade-off before expiry.
What this shows, and what it doesn't
The arithmetic at the close on expiry day, for one contract of 100 shares, before fees. It leaves out what the shares do after you receive them, dividends, and the case of a put (which works the other way: you deliver 100 shares and receive the strike price).