Option Greeks: Delta, Gamma, Theta and Vega explained

Four numbers that say how an option's price will respond before it does. None of them predicts the market; each one answers a narrower, more useful question.

Delta: how much, and which way

Delta is the change in an option's premium for a one-point move in the underlying. A call with a delta of 0.50 gains about half a point when NIFTY rises one point; a put's delta is negative, because puts gain when the market falls. Deep ITM options approach a delta of 1 and trade almost like the underlying; far OTM options sit near 0 and barely react.

Delta is also read as a rough probability: a 0.30-delta option is, loosely, one the market prices with about a 30 percent chance of finishing in the money. Loosely is the operative word; it is a model's shorthand, not a promise.

Gamma: how fast delta itself changes

Gamma is the change in delta per point of movement. It is highest at the money and near expiry, which is why positions there feel twitchy: each move re-prices the next one. Buyers own gamma, so movement helps them. Sellers are short it, so a quiet market is their friend and a fast one is their risk.

Theta: what a day costs

Theta is the premium an option loses per day with everything else unchanged. It is the melt of time value described in the basics guide, given a number. Theta accelerates into expiry, especially for ATM strikes, which is exactly when weekly index options are most actively traded. A buyer pays theta for the chance of a move; a seller collects it for bearing the risk of one.

Vega: the price of expectation

Vega is the change in premium for a one-point change in implied volatility (IV), the market's own estimate of how much movement lies ahead. News, events and nerves raise IV and inflate every premium; calm drains it. An option can lose money on a day the underlying goes the right way, purely because IV came off. That surprise is vega, and it is the Greek most new buyers meet the hard way.

IV also differs across strikes, a pattern called skew. Comparing a strike's IV to its neighbours tells you what the market is paying up for, protection below or chase above.

A position has Greeks too

Every multi-leg strategy nets its legs' Greeks into one set. A straddle starts near zero delta but long gamma and vega, and pays theta for the privilege. A covered call sheds a little delta and collects theta. Reading a position's net Greeks is how traders know what they actually hold, rather than what they meant to build.

Where to watch them move

Greeks are not homework to calculate once; they shift with every tick, and the useful habit is watching them next to price. The option chain here shows the Greeks per strike on market data, and the strategy builder nets them per position, so the numbers in this guide are one click from live practice.

Educational content only: not investment advice. You are responsible for your own trading decisions.