The Greeks measure how an option’s price reacts to the world around it. You don’t need the maths — you need an intuition for each dial.
Delta — direction
Delta is how much the option moves per $1 move in the underlying.
- A delta of 0.50 means the option gains ~$0.50 if the stock rises $1.
- Calls have positive delta (0 to 1); puts have negative delta (0 to −1).
- Handy shortcut: delta ≈ the rough probability the option finishes in the money.
Gamma — how fast delta changes
Gamma is the acceleration — how much delta itself shifts as the stock moves. It’s highest for at-the-money options near expiry, which is why those can swing violently.
Theta — time decay
Theta is how much value the option loses per day from time passing. Negative for buyers (it costs you), positive for sellers (it pays you). You met this as time decay.
Vega — volatility
Vega is how much the price changes per 1% change in implied volatility. Long options are long vega — they gain when IV rises and lose when it falls (the dreaded vol crush).
Rho — interest rates
Rho is sensitivity to interest rates. Usually the smallest Greek and rarely the thing you worry about day to day.
A quick reference
| Greek | Reacts to | Long option |
|---|---|---|
| Delta | price | wants the stock its way |
| Gamma | price (acceleration) | likes big moves |
| Theta | time | loses daily |
| Vega | volatility | likes rising IV |
| Rho | rates | mostly ignorable |
Why bother?
Because two options with the same price can behave completely differently. The Greeks let you say “I’m bullish, but I don’t want much theta or vega risk” — and then pick a strategy that fits. Everything in the strategy library is really just a way of stacking Greeks.