A call option is a contract that gives you the right, but not the obligation, to buy a specific asset at a fixed price before a set deadline, in exchange for an upfront, non-refundable fee called a premium. The seller on the other side of that contract collects the premium and takes on a binding promise to deliver the asset at the agreed price if you decide to buy. Only the seller is bound at the start, which makes the arrangement a one-sided contract until the moment the buyer exercises; from that point, both sides owe each other performance.
Everything else about call options follows from that basic asymmetry. The buyer controls the decision and can lose only the premium. The seller collects the premium up front and lives with the obligation until the contract is closed, exercised, or expires.
The Five Parts of a Call Option Contract
A standardized listed call option has five defined components, and each one matters for how the contract behaves.
- Underlying asset. For standard equity options, one contract covers 100 shares of a specific stock or ETF.1Charles Schwab. Basic Call and Put Options Strategies
- Strike price. The fixed per-share price at which the holder can buy the underlying, regardless of what the stock is trading at in the open market.
- Expiration date. The deadline after which the contract is worthless and the holder’s rights disappear.
- Premium. The non-refundable cash the buyer pays to the seller to open the contract. It is the legal consideration that makes the agreement enforceable.
- Exercise style. American-style options can be exercised on any business day up to and including expiration. European-style options can be exercised only at expiration. Most listed equity options in the U.S. are American-style; many index options are European-style.2The Options Industry Council. What is the Difference Between American-style and European-style Options
Exercise style has real consequences. If you sell an American-style call, you can be assigned at any point before expiration, not just at the end.
Buyer vs. Seller: Who Owes What
The buyer is called the holder. After paying the premium, the holder has three choices: exercise the option and buy the shares at the strike price, sell the option to someone else before expiration, or let it expire worthless. The maximum loss is the premium.
The seller is called the writer. Once the premium is collected, the writer is locked into delivering the shares at the strike price whenever the holder chooses to exercise.3The Options Industry Council. Options Exercise If the writer already owns the 100 shares behind each contract, the position is a covered call, and the only cost of being assigned is losing any gain above the strike price. If the writer does not own the shares, the position is an uncovered or naked call, and the theoretical loss is unlimited because the stock price has no ceiling.4Fidelity Investments. Uncovered Short Call Options Strategy Brokerages require naked call writers to post margin that scales with the stock price under FINRA Rule 4210, and they can force-liquidate the account if the writer cannot meet an increased requirement.5FINRA. FINRA Rule 4210 – Margin Requirements
What Makes the Premium Move
An option’s price at any moment depends mainly on three forces: how the strike compares to the current stock price, how much time is left, and how volatile the market expects the stock to be.
Moneyness
When the stock trades above the strike, the call is “in the money” and has intrinsic value equal to the difference between the two prices. At the strike, it is “at the money.” Below the strike, it is “out of the money” and has no intrinsic value, only whatever time value remains. These labels shift continuously as the stock price moves.
Time Decay
Every option loses value as expiration approaches. The rate of that decay, measured by the Greek letter theta, is not steady. It accelerates sharply in the final weeks and days.6Charles Schwab. Theta Decay in Options Trading An at-the-money option with 60 days left might shed a few cents per day; the same option with five days left can lose several times that daily. Short-dated calls are a fast way to lose money if the stock does not move quickly in the right direction.
Implied Volatility
Implied volatility reflects the market’s expectation of how much the stock will move before expiration. Higher implied volatility pushes premiums up; lower volatility pulls them down. The sensitivity of an option’s price to a 1% change in implied volatility is measured by vega.7The Options Industry Council. Volatility and the Greeks A call can lose value even when the stock moves in your favor, if volatility contracts at the same time.
Exercising, Expiring, and Automatic Assignment
Most options are never formally exercised. Holders typically close the position by selling the contract to someone else before expiration, capturing whatever premium is left. When exercise does happen, the holder notifies their brokerage, which submits an exercise notice to the Options Clearing Corporation (OCC). The OCC randomly assigns the obligation to a clearing member holding a short position, and that member’s brokerage then selects a specific customer account using either a first-in-first-out or random method.8The Options Industry Council. Exercising Options9Nasdaq. Nasdaq PHLX Options 6B – Exercises and Deliveries Settlement for exercised equity options follows a T+1 cycle, so shares and cash change hands the next business day.10OCC. T+1 Equity Settlement Cycle Conversion
At expiration, the OCC’s exercise-by-exception process automatically exercises any equity option that finishes in the money by at least $0.01 per share, unless the holder’s clearing member submits instructions otherwise.11CBOE. OCC Rule Change – Automatic Exercise Thresholds If you hold an expiring call that closes a penny above the strike and do nothing, you will own 100 shares per contract the next business day. The cutoff to override that is 5:30 p.m. Eastern Time on the day of expiration, with brokerages given until 7:30 p.m. ET to submit a Contrary Exercise Advice to the OCC.12FINRA. FINRA Rule 2360 – Options Miss that window and you get the shares whether you can pay for them or not.
One other distinction matters at settlement. Equity and ETF options deliver actual shares. Index options are cash-settled, so no shares change hands; the writer simply pays the holder the cash difference between the strike and the index’s settlement value.13Charles Schwab. Comparing Index Options and Equity Options
Taxes on Call Options
The IRS treats options under 26 U.S.C. § 1234, with results that differ depending on which side of the contract you are on and how the position ends.
If you are the holder and you sell the option before expiration, the gain or loss is a capital gain or loss, short-term or long-term depending on how long you held it. If the option expires worthless, the premium becomes a capital loss on the expiration date.14Office of the Law Revision Counsel. 26 USC 1234 – Options to Buy or Sell If you exercise, there is no separate taxable event for the premium; it is added to the cost basis of the shares you acquire, along with the strike price times the number of shares and any transaction costs.15Charles Schwab. Form 1099-B – Cost Basis and Options Trading The holding period for those shares starts the day after exercise.
If you are the writer, any gain or loss from closing the position or letting it lapse is always short-term, no matter how long the contract was open.14Office of the Law Revision Counsel. 26 USC 1234 – Options to Buy or Sell If the option expires unused, the full premium is a short-term gain on the expiration date. If the option is exercised, the premium folds into the proceeds from the delivered shares.
One trap catches people who think they have cleanly exited a stock. Buying a call on a stock you just sold at a loss triggers the wash sale rule if the purchase falls within the 30-day window before or after the loss sale. The loss is disallowed in the current year and added to the cost basis of the new position instead.16Internal Revenue Service. Publication 550 – Investment Income and Expenses
When Corporate Actions Change the Terms
Stock splits, mergers, and spinoffs do not cancel outstanding option contracts. An adjustment panel from the listing exchanges and the OCC modifies the contract terms to preserve economic equivalence.17The Options Industry Council. Splits, Mergers, Spinoffs and Bankruptcies In a 2-for-1 forward split, a call with a $50 strike becomes two contracts with a $25 strike. In a 1-for-10 reverse split, the strike and contract count usually stay the same, but the deliverable per contract drops from 100 shares to 10. Adjusted contracts often trade under modified ticker symbols with wider spreads and thinner volume, so an unusual option root with a numeral appended is a signal to check what the contract actually delivers before trading it.