Option Greeks are the handful of numbers that describe how an option’s price reacts to the things that move it. Delta measures the reaction to the index, gamma how fast delta itself changes, theta the effect of a day passing, and vega the effect of a change in implied volatility. Each is named after a Greek letter, more or less, which is where the name comes from. You do not need the formulas to use them; you need to know what each one is telling you and how it changes as expiry gets closer. This guide explains the option Greeks in plain words, reads them off a real NIFTY option chain, and shows where the dealer-level versions of the same numbers come in.
Delta: how much the option moves with the index
Delta is how much the option’s price moves for a one-point move in the index, as the Options Industry Council’s delta explainer puts it. A call’s delta runs from 0 to 1 and a put’s from 0 to −1. An at-the-money option has a delta of about 0.5 (or −0.5 for a put); deep in the money it approaches 1, far out of the money it approaches 0. A call with a delta of 0.3 gains about 30 paise for every point NIFTY rises.
Delta has two other everyday uses. It is a rough guide to the chance that the option finishes in the money: a delta of 0.3 is roughly a three-in-ten chance. And it converts an option into an equivalent position in the index: one lot of a 0.5-delta NIFTY call, at 65 units a lot, behaves for small moves like holding about 32 units of the index.
Gamma: how fast delta changes
Gamma is how much delta changes for a one-point move in the index. It is largest for at-the-money options and grows sharply as expiry approaches, because with little time left an option close to the strike flips quickly between being almost worthless and being almost a one-for-one position in the index. Buyers of options are long gamma: their delta moves in their favour as the index moves. Writers are short gamma: their position works against them faster the further the index travels.
Gamma is not a column on the chain in OIData. It appears where it matters most, summed across the market on Dealer Positioning, as gamma exposure by strike and the net figure that decides whether hedging damps or amplifies moves. The gamma exposure guide explains it, and the gamma blast guide shows what expiry-day gamma does to cheap options.
Theta: what a day of time costs
Theta is the premium an option loses per day from time passing alone. It is negative for a buyer and the writer’s daily income. It is largest in rupees for at-the-money options and speeds up as expiry approaches, because time value falls roughly with the square root of the time left. The theta decay guide shows how fast, including what weekends really cost.
Vega: what a point of implied volatility is worth
Vega is the premium gained per one-point rise in implied volatility, and lost per one-point fall. It is largest for at-the-money options and for longer-dated ones, because there is more time for volatility to matter. As expiry approaches, vega shrinks: on the last day, a change in implied volatility moves the price far less than it did a week before. Vega is what turns an IV crush after a budget or results into lost premium.
Reading the option Greeks off a real chain
The figure is the NIFTY chain for the 13 October expiry, a week out, on the morning of 6 October 2026 with the index near 22,630. Read across the at-the-money row, 22650. The call has a delta of about 0.5, so it moves roughly 50 paise for each point NIFTY moves; a theta of about −12, so a quiet day costs its buyer about ₹12; and a vega of 12.7, so a one-point rise in implied volatility adds about ₹12.70. Per lot of 65 units that is about ₹780 of decay a day and about ₹825 for each point of implied volatility. The put row mirrors it: a delta of about −0.5, a similar theta, the same vega.
Now read down the call side. The 22200 call, well in the money, has a delta of about 0.8 and behaves much like the index itself. The 23200 call, more than 550 points above the index, has a delta of about 0.1, a theta of about −5 and a vega of about 5: cheap, slow to lose rupees and barely moved by volatility. Theta and vega are largest at the strikes nearest the index, which is where the option Greeks always concentrate.
How the option Greeks change as expiry approaches
| Greek | A month from expiry | On expiry day |
|---|---|---|
| Delta | Changes gradually across strikes | Close to 1 or 0 for most strikes; only those near the index sit in between |
| Gamma | Small and spread across strikes | Very large at the strike nearest the index |
| Theta | Small, a slow daily drip | Large: the last of the time value goes in hours |
| Vega | Large: volatility has time to matter | Small: little time left for volatility to act |
That table is most of what expiry-day behaviour comes down to: high gamma and high theta together, with vega fading out.
The option Greeks of a whole position
Greeks add up across a position, which is their most practical use. A long straddle, a call and a put bought at the same strike, starts with a delta near zero, positive gamma, negative theta and positive vega: it needs a big move or a rise in implied volatility to pay for the time it loses every day. A short straddle has every one of those signs reversed: it earns theta and loses on big moves and on rising volatility. A futures position has a delta of 1 per unit and no other Greeks at all. Reading a position this way tells you what it needs from the market before you look at a single price.
Beyond the big four: rho, vanna and charm
Rho, the sensitivity to interest rates, matters little for short-dated index options and is rarely shown. Two second-order measures matter more to the desks that hedge options: vanna, how delta changes when implied volatility changes, and charm, how delta changes as time passes. They explain why dealers’ hedging shifts around events and into expiry even when the index is still, and Dealer Positioning ranks both against the index’s own history beside gamma.
Where to read option Greeks in OIData
- The Option Chain adds delta, theta and vega for every strike when its Greeks switch is on; hovering each column heading gives its definition.
- Dealer Positioning shows gamma exposure by strike, and can switch the map to delta, vanna or charm; its IV shock and time sliders re-price the picture for a change in volatility or the passing of time.
- The Volatility page shows the implied volatility that every Greek is calculated from: IV rank, the skew and the term structure.
- The Expiry Day page shows theta and gamma at work on the last day of a contract.
Option Greeks FAQ
What are option Greeks? Measures of how an option’s price reacts to the index (delta), to changes in delta (gamma), to time passing (theta) and to implied volatility (vega).
Which option Greek matters most for a buyer? All four, for different reasons: delta for direction, theta for what waiting costs, vega for what a change in volatility does, and gamma for how quickly all of that can change.
What does a delta of 0.3 mean? The option moves about 0.3 points for each point the index moves, and has roughly a 30 percent chance of finishing in the money.
Why do Greeks differ between apps? They are model estimates calculated from the option’s price, the index, the time left and an interest rate. Different inputs and conventions give slightly different values; the direction and size should agree.
Do option Greeks change during the day? Yes, continuously, with every move in the index, in implied volatility and in the time left. On expiry day they change fastest of all.
Takeaways
- Delta is the move per index point, gamma the change in delta, theta the cost of a day, vega the value of a point of implied volatility.
- At the money, delta is about 0.5 and gamma, theta and vega are near their largest.
- Toward expiry, gamma and theta grow while vega shrinks.
- Greeks add up across a position: a straddle’s signs tell you what it needs from the market.
- On OIData the option Greeks sit in two places: the chain shows delta, theta and vega per strike; Dealer Positioning shows gamma, vanna and charm across the market.