TL;DR: A stock option is a contract giving you the right—but not the obligation—to buy (call) or sell (put) 100 shares of a stock at a fixed price before a set expiration date. You pay a premium upfront. Understanding just five concepts—strike price, expiry, intrinsic value, extrinsic value, and moneyness—unlocks every options strategy you will ever encounter.
What Is a Stock Option?
A stock option is a derivative contract: its value is derived from an underlying asset, usually a stock or ETF. The buyer of an option pays a premium to the seller (called the “writer”) in exchange for the rights spelled out in the contract.
Two things make options fundamentally different from stocks:
- They have an expiration date. After that date, an unexercised option is worthless.
- They convey a right, not ownership. Buying a call on Apple does not mean you own Apple shares—it means you have the right to buy them at a specific price.
In the U.S., each standard equity options contract controls 100 shares of the underlying stock. So when you see a quoted premium of $4.00, the actual cost per contract is $400 (100 × $4.00). This is established by the Options Clearing Corporation (OCC), which clears and guarantees all U.S.-listed equity options.
The Two Types: Calls and Puts
There are exactly two types of options contracts:
Call option — gives the buyer the right to buy 100 shares at the strike price before expiry. Call buyers profit when the stock rises above the strike price.
Put option — gives the buyer the right to sell 100 shares at the strike price before expiry. Put buyers profit when the stock falls below the strike price.
On the other side of every option is a seller (the “writer”) who collects the premium but takes on the obligation to fulfill the contract if the buyer chooses to exercise. Writing options is an advanced topic; beginners should focus on buying first.
The Four Terms You Must Know
1. Strike price (also called exercise price): The fixed price at which you can buy (call) or sell (put) the underlying stock. If XYZ trades at $100 and you hold a $95 call, you can buy 100 shares for $95 each—regardless of where XYZ is trading that day.
2. Expiration date: The last day the option can be exercised or traded. U.S. equity options expire on Fridays. Monthly options traditionally expire on the third Friday of each month; weekly options expire every Friday. After the close on expiration day, an unexercised option ceases to exist.
3. Premium: What you pay (as buyer) or receive (as seller) for the option. Quoted on a per-share basis; multiply by 100 for the total contract cost.
4. Underlying: The stock (or ETF, index, futures contract, etc.) the option references.
In-the-Money, At-the-Money, Out-of-the-Money
These terms describe where the current stock price sits relative to the strike price:
- In-the-money (ITM): A call is ITM when stock price > strike; a put is ITM when stock price < strike. ITM options have intrinsic value.
- At-the-money (ATM): Stock price ≈ strike price. No intrinsic value, but typically the highest extrinsic (time) value.
- Out-of-the-money (OTM): A call is OTM when stock price < strike; a put is OTM when stock price > strike. No intrinsic value—pure time value.
Intrinsic Value vs. Extrinsic (Time) Value
Every option premium has two components, and understanding the split is essential:
Intrinsic value is the amount the option is worth if exercised right now:
- For a call: max(0, Stock Price − Strike Price)
- For a put: max(0, Strike Price − Stock Price)
Extrinsic value (time value) is the portion of the premium that reflects the possibility the option gains additional intrinsic value before expiry. It depends on:
- Time remaining: More time = more opportunity for the stock to move = higher extrinsic value.
- Implied volatility (IV): The market’s expectation of future price swings. A more volatile stock has more potential to move through the strike, so its options carry a larger extrinsic premium.
Formula: Extrinsic Value = Premium − Intrinsic Value
Think of it this way: intrinsic value is the chips you already have in front of you at a poker table. Extrinsic value is the seat fee you paid just to play—it erodes to zero as the clock runs out, regardless of whether you win. This daily erosion is called theta decay, and it is covered in depth in the Options Greeks article.
A Worked Example: The $95 Call on XYZ
XYZ stock trades at $100. You buy one call option:
- Strike price: $95
- Expiry: 30 days from today
- Premium: $7.00 per share → $700 per contract
At purchase:
- Intrinsic value = $100 − $95 = $5.00
- Extrinsic value = $7.00 − $5.00 = $2.00
- Break-even at expiry = $95 + $7 = $102
Scenario A — Stock rises to $110 at expiry:
Intrinsic = $110 − $95 = $15. Profit = ($15 − $7) × 100 = +$800
Scenario B — Stock stays at $100 at expiry:
Intrinsic = $5. Loss = ($5 − $7) × 100 = −$200 (you were right about direction, but not magnitude)
Scenario C — Stock falls to $90 at expiry:
Call expires out-of-the-money. Loss = −$700 (the full premium paid—and the maximum possible loss)
| Strike | Premium | Intrinsic Value | Extrinsic (Time) Value | Moneyness |
|---|---|---|---|---|
| $90 | $11.50 | $10.00 | $1.50 | Deep ITM |
| $95 | $7.00 | $5.00 | $2.00 | In-the-money (ITM) |
| $100 | $4.00 | $0.00 | $4.00 | At-the-money (ATM) |
| $105 | $2.00 | $0.00 | $2.00 | Out-of-the-money (OTM) |
| $110 | $0.75 | $0.00 | $0.75 | Deep OTM |
How Premium Splits Between Intrinsic and Time Value
The chart below shows how the total premium changes across strikes, and how the mix shifts. Deep ITM options (like the $90 strike) are mostly intrinsic value—you’re paying roughly what the option is worth right now. Deep OTM options (like $110) are pure time value: a bet on future movement with no current worth.
Why Investors Use Options
Leverage: Controlling 100 shares of a $100 stock for a $700 premium is far less capital than $10,000 to buy shares outright. The tradeoff: the entire $700 is at risk, and the option expires. Leverage cuts both ways.
Hedging: Buying put options on stocks you already own creates a floor on losses—sometimes called a “protective put.” You pay a premium to insure your position, much like paying an insurance premium on a house.
Income: Selling covered calls—writing call options against shares you own—lets you collect premium in flat or slowly rising markets. It is one of the most common options strategies for individual investors.
Common Mistakes Beginners Make
1. Buying far OTM options as lottery tickets. A $110 call on a $100 stock has a low probability of expiring ITM within 30 days. Most of the premium is time value, which evaporates daily even if the stock trends up slowly.
2. Ignoring theta decay. Being right about direction is not enough—you also have to be right about timing. An option that needs the stock to reach $110 in 30 days will bleed value every day the stock stalls at $103.
3. Buying into high implied volatility. Options are expensive before major catalysts (earnings, FDA decisions, macro events). When the event passes and uncertainty resolves, IV compresses sharply. The option can lose value even if the stock moves your way—a phenomenon called IV crush.
4. Not knowing expiry mechanics. U.S. equity options that are at least $0.01 in-the-money at expiry are automatically exercised by the OCC. If you hold ITM options into expiry, you will receive (or be assigned) 100 shares—which requires capital you may not have. Always close or roll options before expiry if you don’t want exercise.
What to Learn Next
Options 101 is just the foundation. The natural next steps are:
- The Greeks (delta, gamma, theta, vega): how option prices respond to changes in stock price, time remaining, and implied volatility—the four inputs that drive every options position.
- Covered calls: writing calls against shares you own to generate income in sideways markets.
- Protective puts: buying puts to insure a long stock position.
- Vertical spreads: combining a long and a short option to cap both risk and reward.
Each of those strategies is just the call/put/strike/expiry/intrinsic/extrinsic logic above, applied twice.
Sources
- Options Clearing Corporation (OCC) — Characteristics and Risks of Standardized Options (the official options disclosure document for all U.S.-listed equity options).
- CBOE Options Institute — free courses, articles, and tools from the world’s largest options exchange.
- SEC Office of Investor Education and Advocacy — Investor.gov — plain-language investor education on derivatives and options risk.
- CFA Institute, Derivatives curriculum — authoritative textbook treatment of option pricing, intrinsic and time value, and the Greeks.
Disclosure: This article was produced with AI assistance and reviewed before publication. It is for informational purposes only and is not investment advice.