Option Greeks explained: Delta, gamma, theta and vega

An option's price doesn't move in isolation. It shifts in response to changes in the underlying asset's price, the passage of time and the market's volatility expectations. The Greeks (delta, gamma, theta and vega) are sensitivity measures that quantify each of those responses. In this article, you'll follow a single BTC call option as price, time and implied volatility (IV) change, so you can see every Greek in context.

Key Takeaways:

• Delta and gamma describe how an option's price sensitivity changes as the underlying moves.

• Theta and vega describe sensitivity to passing time and changes in the model's volatility input.

• Greeks are estimates at a point in time, not fixed daily results or probabilities of profit.

What do option Greeks measure?

Each Greek measures an option's sensitivity to a particular factor in an options pricing model. Delta, theta and vega estimate changes in option value, while gamma measures how delta itself changes as the underlying moves.

Selling the same option reverses the position's exposure: a short call, for example, has negative delta and negative vega.

To make each Greek concrete, we'll use the same hypothetical position throughout: a 0.1 BTC long call with BTC at $100,000, a $100,000 strike and 30 days to expiry.

Delta and gamma: how a BTC price move affects an option

Delta is a first-order, local estimate. It tells you how much the option's modeled value is expected to change for a small move in the underlying, assuming all other inputs stay constant. For the hypothetical 0.1 BTC call, suppose the model outputs a delta of +0.50. If BTC rises by $100, the model estimates roughly $50 of additional option value per full BTC of underlying, or about $5 for the 0.1 BTC position. That figure is a local model estimate, not realized profit and loss: fees, bid–ask spreads and changes in other variables all affect the price you can actually trade at.

You may encounter the shorthand that delta approximates the probability of an option expiring in the money. Treat this as a rough, model-dependent heuristic rather than a real-world probability or a probability of profit. A delta of 0.50 does not mean a 50% chance that the trade will be profitable.

Gamma explains what happens to delta itself as BTC moves. As BTC moves, the call's delta may also change, so the effect of the next price move won't necessarily match the first. Gamma measures that change in delta. Gamma is typically highest near the money. For near-the-money options, gamma can also become more pronounced as expiry approaches.

Theta and vega: how time and IV affect the same option

Theta estimates how much the call's modeled value declines as one day passes, with all other inputs held constant. A typically negative theta for a long option reflects the fact that the remaining time for the underlying to move favorably is shrinking. For our 0.1 BTC at-the-money call with 30 days left, theta might be relatively moderate; time decay isn't linear and can become more pronounced as expiry approaches, particularly for options near the money. Theta is neither a fixed daily charge nor a guarantee that the option's market price will fall tomorrow: a large enough move in BTC or a spike in IV could offset the passage of time.

Vega measures sensitivity to a one-percentage-point change in implied volatility (IV), not a 1% relative change. In live markets, IV is the volatility level implied by observed option prices through a pricing model. For example, a positive vega means the option's modeled value would generally rise if IV increases by one percentage point, all else equal. All else equal, longer-dated options generally have greater vega than shorter-dated options.

How to read option Greeks together on Bybit

Return to the same BTC call. Suppose BTC rises. As BTC rises, positive delta contributes to the call's increase in value, while positive gamma means delta may also increase, making the position more sensitive to further price moves. At the same time, the passage of time can weigh on the position through theta, while a fall in IV could reduce modeled value through vega. Whether the position shows a net gain or loss depends on which effects dominate and by how much.Position-level Greek exposure scales with quantity. Holding 1 BTC of option quantity instead of 0.1 BTC would multiply the position-level sensitivities by ten, all else equal. The price changes estimated using the Greeks are not executable bid or ask prices. Actual trading prices reflect the order book's bid–ask spread and available liquidity.

On Bybit, you can view each option's Greeks directly. The Option Chain page displays the delta column for every listed strike: calls on the left, puts on the right. When you select a contract and move to the Order Zone, delta, gamma, vega and theta are all shown alongside the order entry.

What option Greeks cannot predict

Greeks change as the underlying price, time and IV change. They are local sensitivity estimates, valid at a specific moment and under specific model inputs. They do not capture every factor that affects the price you can actually trade at or the profit and loss you ultimately realize.

Bid–ask spreads, trading fees and liquidity constraints all create a gap between the model's theoretical value and the price available in the order book. A tight model estimate means little if the contract trades with a wide spread or limited depth. Greeks also cannot tell you whether an option is "good value," whether IV is high or low relative to history, or whether a position will end up profitable. They describe how the model expects a price to respond to isolated changes, not whether those changes will occur or whether the resulting trade will generate a net gain after all costs.

The bottom line

Delta, gamma, theta and vega each isolate one dimension of an option position's risk. Read together, they show where the position is most sensitive and where the largest offsets could come from. Before considering a trade, pull up a Bybit Options contract, inspect its displayed Greeks and think through which variables matter most for your view on BTC's next move.

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