Option Greeks Explained: Delta, Gamma, Theta, Vega
What are option Greeks?
Option Greeks are measures of how an option's price responds to the things that drive it: the underlying price, time, volatility and interest rates. Each Greek isolates one factor while holding the others still.
They come from option pricing models such as Black-Scholes, which Indian brokers and NSE option chains use to show Greeks next to each strike. You do not need the maths to use them. You need to know what each one means in rupees and how it changes as price moves and expiry approaches.
The four that matter most for NIFTY and BANKNIFTY traders are delta, gamma, theta and vega. Rho, the sensitivity to interest rates, is small for short-dated options.
Gamma ≈ change in delta / change in underlying price
Theta ≈ change in option price per day, all else equal
Vega ≈ change in option price per 1 percentage point change in implied volatility
Delta: direction and probability
Delta tells you how much the option price moves for a 1-point move in the underlying. A call with delta 0.50 gains about 0.50 points when NIFTY rises 1 point. Put deltas are negative: a put with delta −0.40 gains about 0.40 when NIFTY falls 1 point.
Delta by moneyness
- At-the-money (ATM) options have delta near ±0.50.
- In-the-money options move towards ±1.
- Far out-of-the-money options move towards 0.
Delta as a rough probability
Traders often read delta as an approximate chance of the option expiring in the money. A 0.20 delta call is loosely a 20% chance. It is an approximation, not an exact probability.
Position delta
Multiply delta by lot size and number of lots to get position delta: how many units of the underlying your position behaves like. It is the basis of delta hedging, where a trader offsets option delta with futures.
Gamma: how fast delta changes
Gamma is the rate of change of delta. If a call has delta 0.50 and gamma 0.002, a 10-point rise in NIFTY lifts delta to about 0.52.
Gamma is highest for ATM options and rises sharply as expiry approaches. That is why weekly options on expiry day can swing from near-worthless to large gains or losses in minutes: delta is changing extremely fast.
Option buyers are long gamma, which helps them when price moves a lot. Option sellers are short gamma, which hurts them when price moves fast. The market-wide version of this idea is covered in gamma exposure (GEX).
Theta: time decay
Theta is how much value an option loses per day from the passage of time, all else equal. It is negative for option buyers and positive for option sellers.
Theta decay is not linear
Time value decays slowly when expiry is far and quickly in the last days. For weekly NIFTY options, decay is steep on the final two sessions, and ATM options lose the most rupees of time value.
Theta and gamma are linked
High gamma and high theta come together. An option buyer pays theta every day for the right to benefit from gamma; a seller collects theta while carrying gamma risk. There is no free side.
Vega: sensitivity to volatility
Vega tells you how much the option price changes for a one-percentage-point change in implied volatility. If an option has vega 8 and IV rises from 14% to 15%, the option gains about 8 points.
Vega is larger for longer-dated options and for ATM strikes. That is why monthly options react more to volatility changes than weekly options. It also explains IV crush: after an event such as a policy announcement or results, IV can drop and option prices fall even if the underlying moved in the expected direction.
Rho and the minor Greeks
Rho measures sensitivity to interest rates. For short-dated index options it is tiny and most traders ignore it.
Advanced traders also watch second-order Greeks such as vanna (how delta changes with volatility) and charm (how delta changes with time). These help explain why option deltas drift late in the day near expiry even when price is flat.
Option Greeks summary table
| Greek | Measures | Highest for | Long option | Short option |
|---|---|---|---|---|
| Delta | Price change per 1-point move | Deep ITM | Directional exposure | Opposite exposure |
| Gamma | Change in delta | ATM near expiry | Positive | Negative |
| Theta | Daily time decay | ATM near expiry | Pays | Earns |
| Vega | Change per 1% IV | ATM, longer expiry | Gains if IV rises | Gains if IV falls |
Worked example: Greeks on a NIFTY option
Illustration with plausible numbers; real Greeks depend on the model and live IV.
NIFTY is at 24,500 with four days to weekly expiry. The 24,500 call trades at 120 with delta 0.52, gamma 0.0025, theta −14 and vega 9.
- If NIFTY rises 40 points quickly, delta adds about 21 points, and gamma lifts the gain a little more, so the call may trade near 142.
- If NIFTY stays flat for a day, theta removes about 14 points, taking it towards 106.
- If IV falls 2 points after an event, vega removes about 18 points.
In practice all three happen together. A buyer can be right on direction and still lose if the move is slow and IV drops. A seller can collect theta for days and give it all back in one fast move. Greeks make these trade-offs visible.
How traders use option Greeks
- Choosing strikes: delta helps choose how directional a position is.
- Sizing: position delta and gamma show how big the exposure really is, which feeds position sizing.
- Timing: theta shows the daily cost of waiting.
- Event risk: vega shows exposure to volatility changes around events.
- Strategy design: straddles are delta-neutral but long or short gamma and vega.
Common mistakes with option Greeks
- Treating Greeks as fixed. They change every tick.
- Ignoring gamma on expiry day. Small moves create large P&L swings.
- Buying options before events without thinking about vega. IV crush can offset a correct view.
- Selling far OTM options because theta looks safe. Low delta is not low risk if gamma spikes.
- Comparing Greeks across expiries without context. Weekly and monthly Greeks behave very differently.
Seeing it on the TradingMarble chart
The TradingMarble app includes a live option chain for NIFTY, BANKNIFTY and the F&O stocks it covers, alongside the price chart and open interest, so you can relate option prices to where the underlying is trading. The features page lists what is shown.
Option Greeks checklist
- Know the delta of the strike and your total position delta.
- Check gamma, especially in the last two days to expiry.
- Know your daily theta cost or income.
- Check vega before events and results.
- Re-check Greeks after big moves; they will have changed.
Option Greeks explain why option prices move the way they do. Trading F&O carries a high risk of loss, and understanding delta, gamma, theta and vega is a basic part of managing it.
Frequently asked questions
What are the option Greeks in simple words?
Delta shows how much an option moves when the underlying moves one point. Gamma shows how fast delta changes. Theta shows how much value the option loses each day from time decay. Vega shows how much it changes when implied volatility moves one point. Rho shows sensitivity to interest rates.
What is a good delta for buying options?
There is no single good delta; it depends on the goal. ATM options near 0.50 delta balance cost and responsiveness. Higher delta options behave more like the underlying and cost more. Low delta options are cheap but need a large move and decay quickly. Choose based on risk, not on price alone.
Why does theta increase near expiry?
Time value does not decay evenly. With many days left, a day is a small fraction of the remaining time. Near expiry each day is a large fraction, so ATM options lose time value much faster. For weekly NIFTY options, theta is steepest in the last two sessions.
What does high gamma mean?
High gamma means delta changes quickly as price moves, so the option's sensitivity to the underlying shifts fast. ATM options close to expiry have the highest gamma. For buyers it can magnify gains on a fast move; for sellers it can magnify losses.
What is vega in options and why does IV crush hurt?
Vega is the change in option price for a one-point change in implied volatility. Before events, IV is often high. Once the event passes, IV usually falls, and the drop multiplied by vega reduces option prices. That is IV crush, and it can offset a correct directional view.
Does NSE show option Greeks?
NSE's option chain shows prices, open interest, volume and implied volatility. Many brokers and charting platforms calculate delta, gamma, theta and vega from those inputs using pricing models. Values can differ slightly between platforms because of model and input choices.