How Stock Options Work: Calls, Puts, Premiums, and Why Most Beginners Lose

A stock option is a contract that gives its buyer the right, but not the obligation, to buy or sell a stock at a fixed price on or before a set date. A call is the right to buy; a put is the right to sell. The buyer pays the seller an upfront price called the premium, and if the stock doesn’t move far enough, fast enough, the option expires worthless and the premium is gone.

In short: an option has four key terms: the underlying stock, the strike price (the price at which you can buy or sell), the expiration date, and the premium (what the option costs). In the US and Canada, a standard equity option contract usually covers 100 shares, so a premium quoted at $2.00 costs $200 per contract. Buyers can lose 100% of what they pay. Sellers collect the premium but take on obligations that can produce large losses.

This article is deliberately introductory. Options strategies, pricing models, and the “Greeks” are beyond its scope.

The basic terms

Term	Meaning
Underlying	The stock the option is on.
Call	Right to buy the underlying at the strike price.
Put	Right to sell the underlying at the strike price.
Strike price	The fixed price in the contract.
Expiration	The last day the option exists. Many stocks have options expiring weekly, monthly, and further out.
Premium	The price of the option, quoted per share. Multiply by 100 for one contract.
Exercise	Using the right: buying (call) or selling (put) at the strike.
Assignment	The seller’s side: being required to sell (call) or buy (put) at the strike.

Most US-listed stock options are American-style, meaning they can be exercised any time before expiry. Most people who trade options never exercise; they sell the option before it expires.

Who stands behind the contract

Listed options trade on options exchanges, and every trade is cleared through a central clearing house that becomes the buyer to every seller and the seller to every buyer. In the US that is the Options Clearing Corporation (OCC). In Canada, equity options trade on the Montreal Exchange and are cleared by the Canadian Derivatives Clearing Corporation (CDCC). The clearing house guarantees performance, so you don’t depend on the particular trader on the other side.

Calls: a worked example

Maple Widgets Inc. (a hypothetical company) trades at $50. You buy one call with a strike of $55 expiring in two months, for a premium of $2.00.

Cost: $2.00 x 100 = $200 (plus any commission).
Break-even at expiry: strike plus premium = $55 + $2 = $57.

Value at expiration:

Stock price at expiry	Call value per share	Value of 1 contract	Profit or loss
$45	$0	$0	minus $200
$50	$0	$0	minus $200
$55	$0	$0	minus $200
$57	$2	$200	$0
$60	$5	$500	+$300
$65	$10	$1,000	+$800

Compare buying 100 shares for $5,000. At $60 you’d be up $1,000 (20%). The call made $300 on $200 (150%). At $55, the shares are up $500 while the call has lost everything. The option needs the stock to rise more than 14% in two months just to break even. That is the core trade-off: options give leverage, but only if you are right about direction, size, and timing.

Puts: a worked example

The stock is at $50. You buy one put with a strike of $45, expiring in two months, for $1.50.

Cost: $150.
Break-even at expiry: strike minus premium = $45 minus $1.50 = $43.50.

Stock price at expiry	Put value per share	Value of 1 contract	Profit or loss
$50	$0	$0	minus $150
$45	$0	$0	minus $150
$43.50	$1.50	$150	$0
$40	$5	$500	+$350
$30	$15	$1,500	+$1,350

People buy puts either to bet on a fall or to hedge shares they already own, like insurance: if you own 100 shares and the stock collapses, the put’s gain offsets part of the loss. As with insurance, the premium is lost if nothing bad happens.

What’s inside the premium

An option’s premium has two parts:

Intrinsic value: what it would be worth if exercised right now. A $55 call when the stock is $60 has $5 of intrinsic value. A $55 call with the stock at $50 has none; it is out of the money.
Time value: everything else. It reflects the chance that the option gains value before expiry, which depends mainly on time remaining and the stock’s expected volatility.

Time value shrinks as expiry approaches, a process called time decay. An out-of-the-money option is made entirely of time value, so if the stock just sits still, its value drifts toward zero day by day.

The premium also rises when the market expects big moves, for example right before an earnings report. After the announcement, that “expected volatility” premium often collapses even if the stock moves.

Selling options

Every option bought was sold by someone. Option writers collect the premium upfront and take on the obligation.

A seller of a covered call owns the shares; if assigned, they deliver shares they already have. The risk is giving up gains above the strike.
A seller of an uncovered (naked) call doesn’t own the shares. If the stock soars, they must deliver shares bought at the market price. Like short selling (see how short selling works), the potential loss has no ceiling.
A seller of a put may be required to buy the stock at the strike, even if it has fallen far below.

Brokers require options approval before you can trade at all, and higher approval (with margin) to sell uncovered options.

How you get approved, and the disclosure you’ll receive

In the US, FINRA Rule 2360 requires a broker to specifically approve each customer’s account for options trading before accepting an order, after gathering information about the customer’s finances and experience. Brokers commonly sort permissions into “levels,” but those levels are each firm’s own system, not a FINRA standard. Before or at approval, you’ll receive the options disclosure document, Characteristics and Risks of Standardized Options, published through the OCC. It is long, and it is worth reading the sections on risks.

In Canada, investment dealers regulated by CIRO must similarly approve clients for options trading and provide risk disclosure.

Why most beginners lose

Options can be useful tools for hedging and for specific strategies. But the evidence on how retail options buyers fare as a group is not encouraging.

Spreads are wide. In a 2023 Journal of Finance study, Bryzgalova, Pavlova, and Sikorskaya found that retail investors favour cheaper, short-dated weekly options, which had an average bid-ask spread of 12.6%, and that retail investors lose money on average. A spread that wide means a round trip can cost a large slice of the premium before the stock moves at all. (See the bid-ask spread explained.)
Buying when options are expensive. A study by de Silva, Smith, and So of Stanford and MIT found that retail investors concentrate options purchases before earnings announcements, when premiums are inflated by expected volatility, and lose on average about 5% to 9% of their investment on those trades, and 10% to 14% when expected volatility is highest. The authors trace the losses to overpaying relative to the volatility that actually occurs, paying wide spreads, and reacting slowly after announcements.
Time decay works against buyers. Even a correct view on direction loses money if the move comes too slowly.
Leverage cuts both ways. A small premium controls 100 shares, so it’s easy to take on more exposure than intended.
Brokers earn more on options. The same Journal of Finance research found that brokers earn more from retail options flow than from stock trading, through payment for order flow, which gives them a commercial reason to promote options; see how stock brokers make money.

Some later academic work argues that retail losses in these studies may be overstated by the way trades are classified. The direction of the evidence, especially on trading costs, is consistent across studies.

There is also a behavioural element: options feel like lottery tickets, with small costs and the possibility of a large payoff, and that framing encourages overtrading. Investor behaviour mistakes covers why people overpay for long shots.

What can go wrong

Losing the whole premium. For an option buyer, this is the most common outcome on out-of-the-money options held to expiry.
Unexpected assignment. If you sold an option, you can be assigned early, especially around dividends.
Automatic exercise. Options that finish in the money by a small amount are often exercised automatically at expiry, which can leave you with a stock position (and a margin requirement) you didn’t plan for.
Liquidity. Options on smaller stocks, or with distant strikes, may have very wide spreads and little trading.
Selling uncovered options. A strategy that collects small premiums many times can lose many times that amount in one bad move.

The short version

A call is the right to buy a stock at a set price, a put is the right to sell, and the premium is the price of that right. Each contract usually covers 100 shares. Buyers risk the entire premium and need the stock to move far enough before expiry; sellers collect premiums but can face large or unlimited losses. Research on retail options trading finds that wide spreads and overpaying for expected volatility leave the average retail buyer behind.