TL;DR: A stock option gives you the right — but not the obligation — to buy or sell 100 shares of a stock at a fixed price before a set date. Call options profit when the stock rises; put options profit when it falls. The price you pay for that right is called the premium, which has two parts: intrinsic value (what the option is worth right now) and time value (what you’re paying for the chance it gets better).
What Is an Options Contract?
An options contract is a legally binding agreement that gives the buyer a right without a requirement. Unlike buying stock outright, you’re buying the ability to act — and you can simply let that right expire if it’s not worth using.
Every standard U.S. equity options contract covers exactly 100 shares of the underlying stock. That’s not arbitrary: it’s the unit that makes option pricing tractable. When you see a quote of $3.50 for a call option, the actual cost to buy one contract is $350 (3.50 × 100 shares).
Options trade on exchanges — most U.S. equity options clear through the Options Clearing Corporation (OCC) and trade on venues like Cboe, Nasdaq PHLX, and NYSE American. There are two fundamental types: calls and puts.
Calls vs. Puts
Think of a call option as a reservation. You pay a small fee today to lock in the right to buy 100 shares at a fixed price later. If the stock soars, your reservation is suddenly very valuable. If the stock drops, you simply don’t use it — your loss is limited to what you paid for the reservation.
A put option is the mirror image: it gives you the right to sell 100 shares at a fixed price. Puts are commonly used as insurance. If you own 500 shares of a stock and worry the market might drop, buying five put contracts can cap your downside — similar to paying an insurance premium on your portfolio.
| Feature | Call Option | Put Option |
|---|---|---|
| Right to… | Buy 100 shares | Sell 100 shares |
| Profits when… | Stock price rises above strike | Stock price falls below strike |
| Buyer’s max loss | Premium paid | Premium paid |
| Seller’s max gain | Premium received | Premium received |
| Seller’s max loss | Theoretically unlimited (uncovered) | Strike price minus premium (if stock → $0) |
Strike Price, Expiry, and Moneyness
Two numbers define every options contract: the strike price and the expiration date.
The strike price (also called the exercise price) is the fixed price at which you can buy (call) or sell (put) the underlying shares. If a call has a $150 strike on a stock trading at $160, you could exercise it today and immediately buy at $150 — $10 below market price. That’s a good deal.
The expiration date is the last day the option exists. For standard monthly U.S. equity options, that is the third Friday of the expiration month. Weekly options, which expire on any Friday, have grown popular for short-term trades. After expiration, an unexercised option is worthless — it simply ceases to exist.
The relationship between the stock price and the strike price is called moneyness:
- In-the-money (ITM): The option has intrinsic value — a call when the stock is above the strike, a put when the stock is below the strike.
- At-the-money (ATM): The stock price equals (or is very close to) the strike price.
- Out-of-the-money (OTM): The option has no intrinsic value — a call when the stock is below the strike, a put when the stock is above the strike.
Intrinsic Value vs. Time Value (Extrinsic Value)
Every option premium breaks into two parts:
Intrinsic value is the immediate exercise value — the amount by which an option is in-the-money. For a call option:
Intrinsic value (call) = max(0, Stock Price − Strike Price)
For a put: Intrinsic value = max(0, Strike Price − Stock Price). An out-of-the-money option always has zero intrinsic value.
Time value (also called extrinsic value) is everything else in the premium — the portion you’re paying for the possibility that the option moves further in-the-money before it expires. It equals:
Time value = Option Premium − Intrinsic Value
Think of time value as the ticking clock. The longer an option has until expiry, the more time the stock has to move in your favor — so more time value. As the expiry date approaches, time value erodes. This daily erosion is called theta decay, and it accelerates in the final weeks before expiration.
A Worked Example
Suppose shares of a semiconductor company trade at $140. You look at the options chain and see a $135 strike call expiring in 30 days, quoted at $7.50 per share (so $750 per contract).
Let’s break down that $7.50 premium:
- Intrinsic value: $140 − $135 = $5.00 (the option is $5 in-the-money right now)
- Time value: $7.50 − $5.00 = $2.50 (you’re paying $2.50 for the next 30 days of potential upside)
Now imagine the stock rallies to $155 by expiry. Your call is now $20 in-the-money. You paid $7.50; it’s now worth at least $20. Profit per contract: ($20.00 − $7.50) × 100 = $1,250 — a 167% return on your $750 investment, while the stock itself only moved 10.7%.
That leverage is the appeal of options. But it cuts both ways: if the stock stays at $140 and the option expires with $5 of intrinsic value, you paid $7.50 and received $5.00 — a loss of $250 per contract, even though the stock barely moved.
How Time Value Erodes: Theta Decay
One of the most important — and counterintuitive — aspects of options is that they lose value simply with the passage of time, even if the stock stays flat. This happens because the “window of opportunity” shrinks every day.
The rate of that erosion is called theta. An option with a theta of -0.05 loses approximately $0.05 of time value per day, all else equal. Theta accelerates as expiration approaches — the final two weeks before expiry see the steepest time-value erosion. This is bad news for option buyers holding positions into expiry, and good news for sellers who collected premiums and want them to decay.
American-Style vs. European-Style Options
Most U.S. equity options are American-style, meaning the buyer can exercise at any time up to and including the expiration date. This flexibility is built into the premium — American-style options are worth at least as much as their European-style equivalents.
European-style options can only be exercised on the expiration date itself — not before. Many U.S. index options (such as SPX options on the S&P 500) are European-style. The trade-off is that European-style contracts are easier to price theoretically, but they offer less flexibility to the buyer.
Common Mistakes and When Options Can Work Against You
Options are powerful but can quietly destroy capital. Here are the traps beginners consistently fall into:
- Paying too much time value. A cheap-looking $0.30 option may have 90% time value with only two weeks to expiry. The stock needs to move significantly just for you to break even.
- Confusing “cheap” with “safe.” A $200 contract feels smaller than buying 100 shares — but options can expire at zero. You can lose 100% of your investment even if the stock only declines modestly.
- Ignoring implied volatility. When markets are nervous, option premiums inflate. Buying a call right before an earnings report often means paying a premium that collapses after the announcement — even if the stock rises. This is called an “IV crush.”
- Selling naked calls. Selling a call without owning the underlying stock exposes you to theoretically unlimited losses if the stock spikes. FINRA warns sellers explicitly about this risk.
- Letting options expire worthless without a plan. Near-expiry OTM options are lotteries. Unless you have a specific reason for the trade, you’re better off closing the position for whatever residual value remains rather than holding for a Hail Mary.
Related Concepts to Learn Next
Once you’re comfortable with calls, puts, and premium decomposition, the natural next steps are:
- The Options Greeks — delta, gamma, theta, vega, and rho measure how an option’s price responds to changes in the stock price, time, volatility, and interest rates.
- Options strategies — covered calls, cash-secured puts, spreads, and straddles combine options in structured ways to express specific views or generate income.
- Implied volatility (IV) — the market’s forward-looking estimate of how much a stock will move, extracted from option prices. High IV means expensive options; low IV means cheaper ones.
Sources
- FINRA – Options — definitions of calls, puts, contract size, strike price, intrinsic value, time value, American vs. European style, expiry mechanics, and risk disclosures.
- Cboe Options Institute — exchange-level education on options fundamentals and strategies.
- OIC (Options Industry Council) — free courses and resources on options basics.
Disclosure: This article was produced with AI assistance and reviewed before publication. It is for informational purposes only and is not investment advice.