What Drives an Option’s Price
Five inputs decide every premium. Change one and the price moves — predictably, once you see it.
An optionThe right, not the obligation, to buy or sell at a set price.’s premium isn’t arbitrary — it’s driven by exactly five inputs. Once you know them, an optionThe right, not the obligation, to buy or sell at a set price. price stops being a mystery number and becomes something you can reason about: change one input and you can predict which way the premium moves.
- 1. Underlying price — how far the stock is from the strikeThe fixed price at which an option can be exercised. (drives intrinsic valueWhat an asset is really worth, based on its fundamentals. and deltaHow much an option moves per ₹1 move in the underlying.).
- 2. Strike priceThe fixed price at which an option can be exercised. — the fixed transaction price; together with the underlying it sets moneyness.
- 3. Time to expiry — more time = more premium (more chance to move); this is the source of time value/theta.
- 4. VolatilityThe size of price swings — not their direction. — higher expected movement = higher premium (more chance of a big payoff); the source of vegaHow much an option’s price changes when volatility changes..
- 5. Interest ratesThe price of money — what borrowing costs and saving earns. — a minor input via cost of carry (the source of rhoAn option’s sensitivity to interest-rate changes.).
Notice the deep connection: *these five pricing inputs are exactly what the GreeksNumbers measuring how an option’s price reacts to each factor. measure the sensitivity to.* Underlying price → deltaHow much an option moves per ₹1 move in the underlying./gammaHow fast an option’s delta changes with price.. Time → theta. VolatilityThe size of price swings — not their direction. → vegaHow much an option’s price changes when volatility changes.. Rates → rhoAn option’s sensitivity to interest-rate changes.. The GreeksNumbers measuring how an option’s price reacts to each factor. aren’t a separate topic — they are simply “how much does the premium move when each of these five inputs changes?” So pricing and the Greeks are two views of one thing: the inputs are the dials, the Greeks are how hard each dial pushes the price. And of the five, four are known and fixed (price, strikeThe fixed price at which an option can be exercised., time, rates) — only **volatilityThe size of price swings — not their direction.* must be estimated*, which is exactly why volatility is where all the action, edgeA repeatable, structural reason your trades win over time., and danger in optionsThe right, not the obligation, to buy or sell at a set price. pricing live (the next lessons).
ExampleAn ATMWhere an option’s strike sits relative to the current price. callThe right, not the obligation, to buy or sell at a set price. is ₹100. Bump just the *volatilityThe size of price swings — not their direction. expectation up and it might jump to ₹130 (nothing else changed). Let a week of time pass with everything else flat and it drifts to ₹80. Each input moved the price in a predictable direction — and the size of each move is* the relevant Greek.
Key takeawayFive inputs set every premium: underlying price, strikeThe fixed price at which an option can be exercised., time to expiry, volatilityThe size of price swings — not their direction., and interest ratesThe price of money — what borrowing costs and saving earns. — and these map one-to-one onto the GreeksNumbers measuring how an option’s price reacts to each factor. (the sensitivities to each). Four inputs are known/fixed; only *volatilityThe size of price swings — not their direction.* must be estimated, which is why it’s where the real action lives.
FAQs
Which of the five inputs matters most day to day?
For directional traders, the underlying price (delta) dominates; but *volatility* is the input that catches people out, because it’s the only one that must be estimated and it can swing premiums dramatically (the volatility crush). Time (theta) matters most the closer you are to expiry. Rates rarely matter except for long-dated options.