How a call option works

A call option is a contract tied to an underlying asset. The buyer pays a premium for the right to buy that asset at the strike price by the expiry date. The seller receives the premium and takes the obligation to deliver under the contract terms if the buyer exercises.

This page follows one long call on a European-style teaching sheet, so exercise is considered only at expiry. Standard listed equity option contracts often use a one hundred share multiplier, but every calculation here stays per share. Contract specifications can differ by market and product.

The right matters because the buyer can walk away. If the asset is cheaper in the market than at the strike, exercising would make no sense. If the asset is dearer in the market, the fixed strike has value.

At expiry, the long call's per-share intrinsic value is

$$\max(S-K,0)$$

$S$ is the underlying spot price and $K$ is the strike. When spot is above strike, the right to buy at strike is worth the difference. When spot is at or below strike, the call expires with zero intrinsic value because the buyer does not have to use the right.

With spot at $60 and strike at $55, intrinsic value is $5 per share. With spot at $50 and the same $55 strike, intrinsic value is 0. The formula floors value at zero rather than allowing the exercise value to become negative.

In-the-money, at-the-money and out-of-the-money describe where spot sits relative to strike. They describe exercise value, not total profit, because the premium still has to be counted.

The buyer pays the premium whether the option is exercised or expires unused. At expiry the per-share profit identity is

$$\text{long call profit}=\max(S-K,0)-p$$

where $p$ is the premium per share. A call can finish in the money and still leave a loss if intrinsic value is smaller than the premium. Break-even at expiry is the strike plus the premium. Above that point, each further unit added to spot adds the same unit to per-share profit.

For the call with a $55 strike and $2 premium, expiry at $60 gives $5 of intrinsic value and $3 of profit per share. Expiry at $50 gives 0 intrinsic value and a $2 loss per share. The premium is the maximum loss for the long call buyer under this expiry payoff, assuming no separate trading costs.

Before expiry, a call usually trades for more than its current intrinsic value. The difference is often called time value. There is still time for the underlying price to move, and the chance and size of a favourable move affect what buyers will pay.

More time, greater expected volatility and a more favourable relationship between spot and strike can raise the option premium, with interest rates and expected cash distributions also entering standard pricing models. These inputs affect the market price before expiry. They do not change the intrinsic-value identity at expiry.

Trading introduces a bid-ask spread. A displayed midpoint is not necessarily the price available for the whole order, and a wide spread can be a meaningful part of the premium. Selling the call before expiry and exercising it are different exits, with different cash and timing effects.

A payoff diagram maps each possible expiry spot to an outcome. It does not say how likely each spot is. A call can offer an open-ended upside shape while still having a low probability of finishing above break-even, because the premium and strike determine where profit begins.

The long call also differs from owning the underlying. It can expire, it does not usually receive the underlying's distributions before exercise, and its price responds to time and expected volatility as well as to spot. How stocks work covers the ownership claim beneath an equity call, while risk and return explains why a possible payoff is not an expected return.

The examples hold the premium fixed at purchase and evaluate the contract at expiry. Real option trades also include spreads, commissions, taxes and contract terms. This is educational material, not financial advice.