Rights versus obligations
A call gives the holder the right to buy at the strike price; a put gives the right to sell. The buyer pays a premium up front and can never lose more than that. The seller — the writer — receives the premium and takes on an obligation, with risk that is theoretically unlimited on a naked call.
That asymmetry is the whole instrument. Everything else is pricing it.
What determines the premium
Five inputs, four of which are observable: the price of the underlying, the strike, time to expiry, and interest rates. The fifth is volatility, which is not observable — it is a forecast.
Because the other four are known, an option's price can be inverted to reveal the volatility the market is assuming. This implied volatility is really what options trade on. Buying an option is a bet that the underlying will move more than implied volatility suggests; selling one is a bet that it will move less. Getting the direction right and the volatility wrong is a common and expensive experience.
Time decay
An option is a wasting asset. All else equal, it loses value every day as expiry approaches, and the decay accelerates near the end. The buyer fights this clock; the seller is paid by it.
This is why most bought options expire worthless, and also why selling options looks like an attractive income strategy right up until the move that takes back several years of premiums in an afternoon.
Legitimate uses
Options are genuinely useful tools. A covered call generates income from shares you already hold, at the cost of capping upside. A protective put is insurance against a fall, at a known premium. A collar combines both for little or no net cost. These are conservative applications used routinely by institutions.
The same instrument bought naked and short-dated is among the fastest ways to lose money available to a retail investor, and the zero-day-to-expiry contracts now dominating US volume are closer to a lottery ticket than to a position.
How you would actually trade it
UK retail access to listed equity options is more limited than in the US; several platforms offer it, generally with a suitability assessment and a tiered permission system reflecting strategy risk.
Start by understanding what you are being paid or charged for volatility, not just direction. Check the bid-offer spread — on illiquid options it can be a large fraction of the premium, which makes the position uneconomic before it starts.
Never sell naked calls without understanding that the loss is uncapped. Many brokers will not permit it without substantial margin, for good reason.
What goes wrong
- Unlimited loss on written calls. The one genuinely uncapped risk in common retail products.
- Total loss is the normal outcome for a bought option that finishes out of the money.
- Time decay works against buyers relentlessly.
- Assignment risk. A written option can be exercised against you early, particularly around dividend dates.
- Complexity. Multi-leg strategies have payoffs most people cannot hold in their head, and platforms rarely make the worst case obvious.
This entry describes how a market works. It is not a recommendation, a price forecast, or advice about whether this belongs anywhere near your money. How entries are written.