Definition
An options contract is a standardized financial agreement that gives its holder the right — but never the obligation — to buy or sell an underlying asset at a predetermined price, known as the strike price, on or before a set expiration date. A call contract conveys the right to buy; a put contract conveys the right to sell.
Each listed equity option typically represents 100 shares of the underlying stock. The buyer pays a premium for this right, while the seller (the writer) receives the premium and takes on the matching obligation if the buyer chooses to exercise. That asymmetry — the buyer chooses, the seller is bound — defines the entire risk profile of the instrument and is the source of both its leverage and its precision as a hedging tool.
Why it matters
How it works
The four building blocks and their risk profiles
There are exactly two primitive options — a call and a put — and each can be held in two positions: long (bought) or short (sold or written). The four building blocks are therefore: long call, short call, long put, and short put. Every options strategy ever constructed is a multi-leg combination of these four. Long calls benefit from rising prices; long puts benefit from falling prices. Short calls collect premium and profit when prices stay flat or fall; short puts collect premium and profit when prices stay flat or rise.
The decisive structural feature is the cap on the buyer's loss. A long call or long put holder can never lose more than the premium paid, no matter how far the underlying moves against the position. The writer, in exchange for collecting that premium upfront, takes on potentially large obligations — a naked call writer faces theoretically unlimited losses if the underlying soars. This is why many brokers require significant approval levels before allowing naked writing.
Contract terms and why standardization matters
Every listed options contract is defined by four fixed terms: the underlying asset, the contract type (call or put), the strike price, and the expiration date. These terms are set when the contract is listed and never change during the contract's life. All participants trading the same contract are trading an identical instrument — this is what makes the market liquid. The premium, however, is not fixed; it moves continuously with supply, demand, and the changing value of each of the five inputs that determine it.
When a buyer exercises a call, the writer must deliver 100 shares at the strike price regardless of the current market price. When a buyer exercises a put, the writer must purchase 100 shares at the strike regardless of how far the stock has fallen. If the contract expires unexercised — because it is out of the money and exercising would be irrational — it lapses and the writer keeps the premium. This outcome is the writer's best-case scenario and the buyer's total-loss scenario, occurring on the same expiry date.
The premium as a compressed signal
The price a buyer pays — the premium — is not arbitrary. It compresses five inputs into a single tradeable number. The spot price relative to the strike determines intrinsic value: how much the option would be worth if exercised immediately. Time to expiration determines how much opportunity remains for the underlying to move favourably; more time means more premium. Implied volatility is the market's consensus estimate of how much the underlying is likely to move; higher volatility commands higher premiums for both calls and puts, because the probability of a large move in either direction increases. The risk-free rate has a smaller effect, and dividends matter for calls on dividend-paying stocks. A trader who can identify which of these five inputs is mispriced — particularly implied volatility — has a genuine analytical edge rather than a directional bet.
Understanding what is moving the premium, and by how much, is what separates a deliberate trade from a guess. Beginners often focus on directional prediction alone; experienced traders often focus on the structure of the premium as much as on the underlying's direction.
Options as derivatives: the underlying is everything
An option's value is derived entirely from the underlying asset. There is no intrinsic value in the contract itself — its value lives or dies with the stock (or ETF, index, or commodity) it is written against. Choosing the wrong underlying means no amount of strike or expiration tuning will rescue the trade. This is the most important single variable in any options strategy: where the underlying goes, the option almost always follows in the relevant direction.
This derivation relationship also explains why options are studied alongside the underlying rather than as standalone instruments. A call option on a stock that is trending steadily upward in a narrow channel behaves very differently from the same contract on a stock that is subject to frequent earnings surprises, even if the premiums are initially similar.
Time decay and the buyer-vs-seller dynamic
Options are wasting assets. From the moment a position is opened, the clock runs toward expiration, and the time value component of the premium decays toward zero — the process known as theta decay. This decay is not linear; it accelerates sharply in the final weeks before expiration. Buyers are fighting time; sellers are collecting it. Every strategy is, at some level, a bet on whether time decay will help or hurt.
The covered call — selling a call against shares already held — is the simplest expression of the seller's time-decay advantage. The shareholder collects premium immediately and profits if the stock stays flat or rises to the strike. The trade is described as covered because the shares needed to deliver if the call is exercised are already held in the account; the seller cannot be squeezed by a runaway stock price the way a naked seller would be.