Stock Options Explained: Calls, Puts, and How They're Priced

The Right to Buy or Sell — Without the Obligation

In 2023, U.S. options markets traded an average of 46 million contracts per day — a record that dwarfed trading volumes from just five years prior. Options are among the most versatile financial instruments ever created, used simultaneously by conservative investors hedging portfolios and speculators betting on short-term price swings with leverage.

Calls and Puts: The Two Building Blocks

Every option contract falls into one of two categories. Understanding the distinction is the foundation of all options strategy.

• Call option — gives the buyer the right, but not the obligation, to buy 100 shares of an underlying stock at a specified price (the strike price) before or on the expiration date
• Put option — gives the buyer the right, but not the obligation, to sell 100 shares at the strike price before or on expiration
• Each contract typically represents 100 shares of the underlying asset
• The buyer pays a premium upfront; the seller (writer) receives that premium and takes on the obligation

A call option on Apple with a $200 strike expiring in three months means the buyer can purchase 100 Apple shares for $200 each, regardless of where the stock is trading. If Apple rises to $230, the option has $30 of intrinsic value per share, or $3,000 total. If Apple stays below $200, the option expires worthless and the buyer loses only the premium paid.

Moneyness: In, At, and Out of the Money

Options traders use the term moneyness to describe the relationship between the current stock price and the strike price.

In-the-money options have intrinsic value. Out-of-the-money options consist entirely of time value — the possibility that the stock moves favorably before expiration. At expiration, OTM options are worth zero.

The Black-Scholes Pricing Model

Fischer Black, Myron Scholes, and Robert Merton published the foundational options pricing framework in 1973. Merton and Scholes were awarded the Nobel Prize in Economic Sciences in 1997 (Black died in 1995). The model calculates a theoretical fair value for European-style options using five inputs.

Implied volatility (IV) is the market's forward-looking estimate of how much the stock will move. Unlike historical volatility, IV is derived from actual options prices — it is what the market is implying, not what has happened. The VIX index measures the implied volatility of S&P 500 options, earning its nickname as the market's fear gauge.

The Greeks: Measuring Option Sensitivity

Traders use a set of risk measures called the Greeks to understand how an option's price changes in response to market conditions.

• Delta — change in option price per $1 move in the underlying stock (ranges from 0 to 1 for calls, -1 to 0 for puts)
• Gamma — rate of change of delta; highest for at-the-money options near expiration
• Theta — daily time decay; an option loses value each day even if the stock is unchanged
• Vega — sensitivity to implied volatility; a vega of 0.10 means the option gains $0.10 per 1% rise in IV
• Rho — sensitivity to interest rate changes; generally the smallest Greek in practice

Theta is the enemy of option buyers and the friend of sellers. An option that costs $300 with 60 days remaining may be worth only $180 with 30 days remaining and the stock unchanged — purely from the passage of time.

American vs. European Style Options

American-style options can be exercised any time before expiration. Most equity options traded on U.S. exchanges are American-style. European-style options can only be exercised on the expiration date itself. S&P 500 index options (SPX) are European-style, while options on the SPDR S&P 500 ETF (SPY) are American-style.

Common Options Strategies

Single-leg options — buying a bare call or put — are the simplest form. Multi-leg strategies combine options to define profit and loss more precisely.

• Covered call — owning stock and selling a call against it to generate premium income; caps upside
• Protective put — owning stock and buying a put to insure against decline; reduces loss exposure
• Bull call spread — buying a lower-strike call and selling a higher-strike call; limits both gain and cost
• Iron condor — selling a call spread and put spread simultaneously; profits when the stock stays in a defined range
• Straddle — buying a call and put at the same strike; profits from large moves in either direction

Employee Stock Options vs. Exchange-Traded Options

Employee stock options (ESOs) are not the same as exchange-traded options. ESOs are contractual grants from a company to an employee, giving the right to buy company shares at a fixed grant price. They typically vest over three to four years and have 10-year expiration windows. Unlike exchange-traded options, ESOs cannot be sold or transferred, and they are not standardized instruments.

The Financial Accounting Standards Board's ASC 718 requires companies to expense the fair value of ESOs at grant date, typically using a variation of Black-Scholes.

Risk Profile Summary

The maximum loss for an option buyer is the premium paid — a defined and limited amount. The maximum loss for an option seller of a naked call is theoretically unlimited, because the stock can rise without bound. For a cash-secured put seller, maximum loss equals the strike price minus the premium received, multiplied by 100.

This article is for informational purposes only and does not constitute financial advice.