Direct Answer
An option contract is a legally binding agreement giving the buyer the right — but not the obligation — to buy (call) or sell (put) 100 shares of an underlying asset at a specified strike price on or before an expiration date, for a price called the premium. Six elements define every contract: the underlying asset, the type (call or put), the strike price, the expiration date, the premium, and the contract multiplier (almost always 100 shares for equity options).
Key Takeaways
- Calls grant the right to buy; puts grant the right to sell. The option buyer pays the premium; the option seller (writer) collects it and assumes the obligation.
- The strike price is fixed and determines the price at which the underlying can be bought or sold if the option is exercised.
- The expiration date caps the option's life. After that date, an unexercised option expires worthless; the premium paid is the maximum loss for a long option position.
- Each standard equity option contract controls 100 shares, meaning a $3.00 premium displayed on a screen costs $300 to buy (3.00 × 100).
- The premium is set by the market, not by the exchange. It reflects intrinsic value (how far in the money) plus time value (the remaining uncertainty premium).
- Buyers and sellers have opposite payoff profiles: buyers pay upfront for potentially unlimited upside (calls) or large downside protection (puts); sellers collect premium but assume open-ended obligations.
- The option chain — the listing of all available strikes and expirations for a given underlying — is where traders see every combination available at any moment.
- Exercise and assignment are the mechanisms that convert an option into an equity position; most retail traders close options before expiration rather than exercising them.
Core Concepts
The Underlying Asset
The underlying is the security that the option contract references. For equity options, this is a single stock (e.g., Apple Inc., ticker AAPL) or an exchange-traded fund (e.g., SPY, tracking the S&P 500). Index options reference a market index such as the S&P 500 (ticker: SPX) directly, and because indexes cannot be delivered as shares, they settle in cash at expiration rather than through share transfer.
The choice of underlying matters for several reasons beyond the obvious one of directional exposure. Index options are typically European-style (exercise at expiration only), while individual equity options are American-style (exercise any time before expiration). Liquidity also varies dramatically: SPY and QQQ options trade enormous volume with tight bid-ask spreads, while options on smaller stocks may have wide spreads that impose significant transaction costs on every trade.
ETFs on the same index can have very different option characteristics. SPY, IVV, and VOO all track the S&P 500, but SPY options have the deepest liquidity, smallest bid-ask spreads, and the broadest range of available strike prices and expirations. Understanding which underlying to trade — not just which direction — is a real skill in options market practice.
Call Options
A call option gives the buyer the right to purchase the underlying at the strike price before or at expiration. An investor buys a call when they expect the underlying price to rise above the strike before expiration. If AAPL is trading at $190 and a trader buys a call with a $195 strike expiring in 30 days for a premium of $3.00 per share ($300 total for one contract), the trade is profitable at expiration only if AAPL trades above $198 ($195 strike + $3.00 premium = $198 breakeven).
The call seller (writer) has the opposite view or motivation. By selling the call, they collect the $300 premium and take on the obligation to sell 100 shares of AAPL at $195 if the buyer exercises. If AAPL stays below $195 at expiration, the call expires worthless and the writer keeps the premium as pure profit. If AAPL surges to $220, the writer faces the obligation to sell at $195 regardless — a loss of $25 per share ($2,500) minus the $300 premium collected, for a net loss of $2,200.
Calls are also used without a directional view, for example in covered call strategies where a holder of 100 shares sells a call against the position to generate premium income, accepting a cap on upside in exchange for the premium received. This is one of the most common retail options strategies.
Put Options
A put option gives the buyer the right to sell the underlying at the strike price before or at expiration. An investor buys a put when they expect the underlying price to fall below the strike, or when they want to protect an existing long position against a decline. If AAPL is trading at $190 and a trader buys a put with a $185 strike expiring in 30 days for a premium of $2.50 ($250 total), the trade profits at expiration only if AAPL falls below $182.50 ($185 − $2.50 = $182.50 breakeven).
The put seller collects the $250 premium and takes on the obligation to buy 100 shares of AAPL at $185 if the buyer exercises. If AAPL stays above $185, the put expires worthless and the seller keeps the premium. If AAPL falls to $150, the seller is obligated to purchase shares at $185 when they are worth $150 — a loss of $35 per share ($3,500) minus the $250 premium received, for a net loss of $3,250. This is why cash-secured puts require substantial capital in reserve.
Protective puts are among the most intuitive options strategies: a long stockholder buys puts to floor their downside. If you own 100 AAPL shares at $190 and buy a $180 put, you have guaranteed the right to sell at $180 even if AAPL crashes to $100. The put functions as insurance: the premium is the insurance cost, the strike is the policy deductible.
The Strike Price
The strike price (also called the exercise price) is the price at which the option buyer may buy (call) or sell (put) the underlying upon exercise. Strikes are listed at standardized intervals — often $1, $2.50, or $5 apart for actively-traded stocks, wider for higher-priced underlyings. The full range of available strikes for an underlying and expiration is the option chain.
The relationship between the strike and the current market price defines moneyness, a concept central to understanding both the option's probability of profit and how its price will change. An in-the-money (ITM) call has a strike below the current price; an out-of-the-money (OTM) call has a strike above it; an at-the-money (ATM) call has a strike approximately equal to the current price. The deeper in the money an option is, the larger its intrinsic value component and the smaller its time value component.
Strike selection is a strategy decision, not just a detail. A deep-in-the-money call moves almost dollar-for-dollar with the stock but costs considerably more premium. A far-out-of-the-money call is cheap but has a low probability of expiring in the money. Most traders choose strikes in the range of 0.30 to 0.70 delta for directional plays, balancing cost, probability, and leverage.
Expiration Date and Contract Multiplier
The expiration date is the last day on which the option can be exercised. For standard US equity options, expiration occurs on the third Friday of the expiration month (or the preceding Thursday if that Friday is a holiday). Weekly expirations (introduced widely in the 2000s) expire on each Friday. Daily and even same-day (0DTE — zero days to expiration) options exist on major indexes and ETFs, enabling extremely short-term speculation or hedging.
Time remaining to expiration has a direct and non-linear effect on premium. An option with 90 days remaining will lose time value slowly at first, then increasingly quickly as expiration approaches. This phenomenon — called theta decay or time decay — is a core risk for option buyers and a core profit source for option sellers. The decay accelerates markedly inside 30 days, and especially inside 7 days, which is why many experienced traders avoid holding long options into the final week of life.
The contract multiplier is the factor by which the quoted per-share premium is multiplied to get the actual dollar cost of one contract. For virtually all standard US equity options, this is 100. A premium of $4.50 per share means one contract costs $450. This multiplier is the source of options' leverage: controlling 100 shares at $200 each ($20,000 notional) for only $450 in premium is 44:1 leverage at the notional level, though the more relevant leverage figure compares the option's dollar sensitivity (delta × 100 × underlying price) to the premium paid.
Worked Scenario
Consider a trader analyzing Microsoft (MSFT), currently trading at $420.00. They believe MSFT will rise to around $440 over the next six weeks following an earnings release. Here is how they read and evaluate a specific option contract:
- Identify the underlying: MSFT — an American-style equity option on one of the most liquid single-stock option markets. Bid-ask spreads are typically $0.01–$0.05 on near-the-money strikes.
- Choose the type: A call option, because the directional thesis is bullish (expecting a price rise).
- Select the strike: The $425 call, slightly out of the money. At $420 underlying, a $425 strike is $5 OTM. The option has no intrinsic value yet — the entire premium is time value plus the market's implied probability of moving in the money.
- Choose the expiration: The 42-day (6-week) expiration. This gives the price move time to materialize while limiting the premium spent. The mid-price on the $425 call is $8.50 per share.
- Calculate the total cost: $8.50 × 100 shares = $850 per contract. This is the maximum loss if MSFT stays at or below $425 at expiration.
- Calculate the breakeven at expiration: $425 strike + $8.50 premium = $433.50. MSFT must trade above $433.50 for the position to be profitable at expiration. The target of $440 implies a profit of ($440 − $433.50) × 100 = $650 per contract, a return of 76% on the $850 invested.
- Assess the risk: Maximum loss is $850. The position benefits from MSFT rising, but also loses value each day from theta decay and would lose value if implied volatility contracted after earnings. Both theta and vega risk exist alongside directional risk.
Measurement Framework
| Element | What it tells you |
|---|---|
| Strike price vs. current price (moneyness) | Indicates intrinsic value and probability of expiring in the money; ITM options are more expensive but have higher probability of value at expiration. |
| Days to expiration (DTE) | Controls how much time value exists and how fast theta decay will erode premium; longer DTE = more time value, slower initial decay. |
| Premium / cost of one contract | Premium × 100 = total dollar risk for a long position; this is the maximum loss for any long option trade, defining the risk at entry. |
| Breakeven at expiration | For calls: strike + premium. For puts: strike − premium. The underlying must move beyond this point for the trade to profit at expiration. |
| Bid-ask spread | Measures transaction cost and market liquidity. A $0.50 wide spread on a $3.00 option means 16.7% immediate slippage; avoid wide-spread contracts for frequent trading. |
| Open interest | Number of outstanding contracts at a given strike/expiration. Higher open interest generally corresponds to tighter spreads and easier entry/exit at fair prices. |
| Implied volatility (IV) | The market's embedded expectation of future price movement. High IV = expensive options; low IV = cheaper options. IV changes continuously and affects premium independent of the underlying price. |
Common Failure Modes
Ignoring the Bid-Ask Spread
New options traders often look at the mid-price of an option without accounting for the bid-ask spread. On illiquid options, the bid may be $1.50 and the ask $2.50 — buying at the ask and later selling at the bid costs $1.00 per share ($100 per contract) immediately, a 40–67% round-trip cost before any price movement occurs.
Always check open interest and the bid-ask spread before selecting a strike. Stick to options where the spread is 5–10% or less of the option price, and use limit orders rather than market orders to avoid paying the full spread at entry.
Confusing Leverage with Risk
Options offer significant leverage, which many traders equate with low risk because the dollar amount at stake is small. Paying $200 for a call option can feel like modest risk compared to buying 100 shares. But the probability of losing 100% of that $200 (the entire premium) is much higher than losing 100% on a stock position — because the stock would have to go to zero, while the option just needs to expire out of the money.
The right way to think about option position sizing is: what percentage of the total account does the premium at risk represent? A $200 option on a $10,000 account is 2% at risk, which is a reasonable single-trade risk. Buying 10 such options for $2,000 is 20% of the account at risk on one directional bet, which is not the same as taking a small-risk position.
Buying Options Ahead of High-IV Events
Many new traders buy options before earnings announcements expecting a large move to generate profit. What they miss is that the market prices in the expected move through elevated implied volatility, inflating the premium. After the earnings release, even if the stock moves in the right direction, IV often collapses dramatically — the "IV crush" — causing the option's time value to drop faster than the intrinsic value gained.
The solution is to check the implied volatility percentile or IV rank before buying options ahead of known events. If IV is already in the 80th percentile or higher, buying options is expensive relative to historical norms. Selling premium strategies (credit spreads, iron condors) may be more appropriate in high-IV environments.
Underestimating Theta Decay in the Final Weeks
Theta decay — the daily loss of time value — is not linear. An option with 60 days to expiration decays slowly; the same option with 7 days left can lose 20–30% of its remaining time value in a single day. Traders who buy out-of-the-money options with 30 days to expiration and then hold them through the final week often watch their position evaporate even as the stock moves in the right direction.
As a rule of thumb, consider setting a time stop alongside a price stop on long option positions: decide in advance what you will do if the underlying hasn't moved in your favor by the time 50% of the option's life has elapsed. Selling or rolling at that point typically recovers more value than holding to expiration in a losing scenario.
Confusing Exercise with Closing
Retail traders rarely need to exercise an option to realize a profit. An in-the-money call that has appreciated in value can simply be sold back into the market. Exercising a call early typically destroys the time value remaining in the option — you give up the time premium you paid, receiving only the intrinsic value differential. The exception is when an option has very little time value remaining and a dividend payment is imminent that would benefit the stockholder, making early exercise economically rational.
When a long option position is profitable, the default action should be to close it (sell) through the options market rather than exercise. Only exercise when you specifically want the resulting equity position and the time value remaining is negligible.
FAQ
What is the difference between a call and a put option?
A call option gives the buyer the right to purchase the underlying at the strike price; a put gives the buyer the right to sell at the strike price. Calls benefit when the underlying rises above the strike; puts benefit when it falls below the strike. Both involve the buyer paying a premium and the seller receiving that premium in exchange for the corresponding obligation.
How many shares does one option contract control?
Standard US equity option contracts control 100 shares. A quoted premium of $3.50 means the actual cost of one contract is $350 (3.50 × 100). This is nearly universal for individual stock and ETF options; only mini-options (10 shares, rare) and index options (cash-settled, no share delivery) differ structurally.
What does it mean for an option to expire worthless?
An option expires worthless when it is out of the money at expiration. For a call, this means the underlying closed at or below the strike price; for a put, it closed at or above the strike. The buyer of the option loses 100% of the premium paid. The seller of the option keeps 100% of the premium received as profit. Roughly 70–75% of options held to expiration expire worthless.
Can I lose more than the premium I paid on a long option?
No. The maximum loss on a long option position (buying a call or put) is limited to the premium paid. This is one of the key features distinguishing options from other leveraged instruments like futures, where losses can exceed the initial margin. The defined-risk nature of long options is why they are used for hedging — the cost is known in advance.
What is an option chain?
The option chain is the tabular display of all available call and put options for a given underlying, organized by expiration date and strike price. Each row shows the bid price, ask price, last trade price, volume, open interest, and implied volatility for that specific contract. Most brokerage platforms display the option chain; calls are usually shown on the left, puts on the right, with strikes in the center column.
What happens if I hold an option through expiration?
In-the-money options are automatically exercised at expiration by the broker (under OCC rules, ITM options are exercised unless the holder submits a contrary instruction). For a long call, you would receive 100 shares of the underlying at the strike price. For a long put, you would sell (or be short) 100 shares at the strike. Out-of-the-money options simply expire worthless. Most retail traders close positions before expiration to avoid unwanted equity delivery.
What is the difference between American and European style options?
American-style options can be exercised by the buyer on any business day up to and including expiration. European-style options can only be exercised at expiration, not before. US equity and ETF options are almost all American-style. Most broad index options (SPX, XSP, NDX, RUT) are European-style. The style matters most to sellers of American-style options, who face early assignment risk.
Why is the option premium different from the intrinsic value?
The premium (market price) of an option equals its intrinsic value plus its time value. Intrinsic value is the amount the option is in the money (e.g., if a stock is at $205 and the call strike is $200, intrinsic value is $5.00). Time value is the additional premium attributable to the remaining life of the option, the uncertainty about future price movements, and the level of implied volatility. Out-of-the-money options have zero intrinsic value, so their entire premium is time value.
Sources
Disclaimer
This article is for educational and informational purposes only and does not constitute personalized investment, financial, or legal advice. Options trading involves significant risk, including the possible loss of the entire premium paid. All examples use hypothetical prices and are intended solely for illustration. Verify current contract specifications with your broker or the relevant exchange before trading.