Options basics: calls, puts and what a premium buys

An option is a contract that gives its buyer the right, but not the obligation, to buy or sell a stock at a fixed price before a set date. Buyers pay an upfront price, called the premium, for that right. Options can be used to hedge, to generate income or to speculate, and understanding the basics helps you recognize both their uses and their risks.

The building blocks

• Call option: the right to buy the underlying stock at the strike price.
• Put option: the right to sell the underlying stock at the strike price.
• Strike price: the fixed price at which the stock can be bought or sold.
• Expiration date: the last day the option exists. Standard monthly options expire on the third Friday of the month, and many stocks also have weekly expirations.
• Contract size: one standard equity option typically covers 100 shares.
• Premium: the price of the option, quoted per share. A quote of $2.00 means $200 per contract.

The buyer, or holder, has the rights. The seller, or writer, takes the premium and accepts the obligation: a call seller must deliver shares if the holder exercises, and a put seller must buy them. Most US equity options are American-style, which means they can be exercised at any time up to expiration. Many index options are European-style, exercised only at expiration, and settle in cash.

What the premium is made of

An option is "in the money" when exercising would have value (a call with the stock above the strike, a put with the stock below it), "at the money" when the stock is near the strike, and "out of the money" otherwise.

Call intrinsic value = max(Stock price - Strike, 0)
Put intrinsic value  = max(Strike - Stock price, 0)
Premium              = Intrinsic value + Time value

Time value is what is left over, and it reflects the chance that the option becomes more valuable before expiration. It is larger when more time remains and when the stock is expected to be more volatile, and it shrinks as expiration approaches. This erosion is called time decay. The market's expectation of volatility, called implied volatility, is a key input in option prices. See volatility and the VIX.

Example (illustrative numbers)

A stock trades at $48. You buy one call with a $50 strike that expires in two months for a premium of $2.00. Your cost is $200, which is also the most you can lose as a buyer.

Break-even at expiration = Strike + Premium = $50 + $2 = $52

The stock can rise from $48 to $51, a gain of more than 6%, and you still lose money: at expiration the call is worth only $100 ($1 of intrinsic value times 100 shares), less than the $200 you paid. Being right about direction is not enough. You also need enough of a move, soon enough.

A put works in the mirror image. A put with a $50 strike bought for $3.00 costs $300 and breaks even at $47 ($50 - $3). It gains as the stock falls below that and loses its $300 if the stock stays above $50.

Buyers and sellers

A buyer's loss is limited to the premium, while upside can be large relative to it. A seller's position is the reverse: the gain is limited to the premium, and the potential loss can be large.

• A covered call (selling a call while owning the 100 shares) is a common income strategy. It limits upside above the strike.
• A cash-secured put means selling a put while holding cash to buy the shares if assigned.
• A naked call (selling a call without owning the shares) carries theoretically unlimited loss, much like a short sale. See short selling. Brokers require approval levels and margin for this reason.

How to think about options: rules of thumb

• Options are leveraged: a small premium controls a large exposure, so percentage swings can be extreme. See margin and leverage.
• Buyers fight time decay, since the option loses value each day if the stock does not move enough.
• Wider bid-ask spreads are common in less active contracts, which raises the real cost of trading. See bid, ask and spread.
• Many traders close contracts before expiration rather than exercise them, since selling the option recovers any remaining time value.
• Options can be used to hedge. A put on a stock you own works like insurance, and the premium is the cost of that protection.

Common mistakes

• Buying cheap, far-out-of-the-money options as lottery tickets and treating the low price as low risk. The probability of losing the whole premium can be high.
• Ignoring expiration. A correct view that plays out after the option expires pays nothing.
• Selling options without understanding the loss potential.
• Overlooking dividends and early assignment on short American-style options.
• Forgetting earnings dates. Option prices often embed expected volatility around announcements, and implied volatility can drop sharply afterward.

Where this fits on StocksXray

StocksXray does not carry options data, so this article is background to help you understand the instruments that trade alongside the stocks you research. The site's focus is on fundamentals, valuation and price-based technical signals for US stocks.

Key takeaways

• A call is the right to buy and a put is the right to sell at a fixed strike price before expiration.
• Premium equals intrinsic value plus time value, and time value decays as expiration nears.
• A buyer's maximum loss is the premium, and a seller's potential loss can be much larger.
• Break-even is strike plus premium for a call and strike minus premium for a put.