Option Greeks Basics: Delta, Theta, Vega for Indian Markets

Plain-English guide to the four main option Greeks — Delta, Theta, Vega, Gamma. India-specific examples using NIFTY and BANKNIFTY.

3 November 2024 · 9 min read

The option Greeks are sensitivity measures — they tell you how much an option's price will change when one input changes. There are four you need to know: Delta, Gamma, Theta, Vega. A fifth, Rho, exists but is rarely material for short-dated Indian options.

If you're brand new to options, read Call Options Explained and Put Options Explained first.

Delta: how much the option moves when the underlying moves ₹1

Delta is the most intuitive Greek. It ranges from 0 to +1 for calls and −1 to 0 for puts.

An at-the-money NIFTY call typically has delta around +0.50. If NIFTY rises by 100 points, the call premium rises by roughly 50 points.
A deep-in-the-money call has delta close to +1.00 — it behaves almost like the underlying.
A deep-out-of-the-money call has delta near +0.05 — it barely moves with NIFTY.

For puts, the signs flip. An ATM put has delta around −0.50.

Delta is also a rough probability estimate of the option finishing in-the-money. A 0.30-delta call has roughly a 30% chance of expiring ITM (very rough — assumes lognormal distribution).

Gamma: how fast Delta changes

Gamma measures the curvature. Delta isn't constant — it changes as the underlying moves. Gamma is highest for at-the-money options near expiry. This is why short-dated ATM options are explosive: a tiny move in NIFTY produces a big change in delta, which produces an outsized change in premium.

Gamma is great for buyers (you get accelerating profits when right) and brutal for sellers (losses accelerate when wrong). India's weekly expiries — NIFTY on Thursdays, BANKNIFTY on Wednesdays — concentrate gamma risk into the last 24 hours of the contract.

Theta: how much value you lose each day

Theta is the dollar amount the option loses every day from time decay alone, assuming all other variables stay fixed.

A NIFTY ATM weekly option might have theta of −15 per day when 5 days from expiry, and −40 per day the day before expiry.
Theta accelerates as expiry approaches. The last week's decay is roughly equal to the entire previous month's decay.

This is why buying options the week of expiry is statistically a losing proposition unless you have a strong, fast catalyst (e.g., a Budget announcement). Theta works against you every minute.

Vega: sensitivity to implied volatility

Vega tells you how much the premium changes when implied volatility (IV) moves by 1 percentage point.

A NIFTY ATM monthly option might have vega ≈ 25. If IV rises from 12% to 13%, premium rises by ₹25 × 75 = ₹1,875 per lot.
Vega is highest for ATM options with the most time to expiry. Weekly options have very low vega; long-dated options have high vega.

This matters for India around scheduled events: IV pumps up before Budget, RBI policy, US Fed decisions, and big earnings. After the event, IV collapses — the famous "IV crush." Even if the underlying moves in your direction, vega losses can wipe out gains.

Putting the Greeks together

A typical retail trade: buy an OTM NIFTY weekly call on Monday for ₹50.

| Greek | Approximate value | What it means | |---|---|---| | Delta | 0.20 | NIFTY +100 pts → premium +20 | | Gamma | 0.005 | Delta will accelerate if NIFTY rallies | | Theta | −10/day | You lose ₹10/unit/day from decay | | Vega | 5 | IV +1% → premium +5 |

If NIFTY is flat for two days, you lose roughly ₹20 from theta alone. To break even, NIFTY needs to rally enough to overcome the daily theta drain — typically 50-100 points just to tread water.

Greeks for selling strategies

Sellers profit from theta but carry vega risk. A short straddle (selling ATM call + ATM put) has:

Delta near zero — direction-neutral
Negative gamma — directional moves hurt
Positive theta — profits accrue daily
Negative vega — IV spikes hurt

Most consistent institutional options income strategies are negative-gamma / positive-theta trades. They make small amounts most days and occasionally have large losses.

Where to read live Greeks

NSE's option chain doesn't display Greeks directly. To compute them you need:

Spot price (live from NSE)
Strike, expiry, IV (from option chain)
Risk-free rate (use 6-month T-Bill yield, ~6.5% as of late 2024)
Black-Scholes formula (or binomial for American-style — though NSE options are European)

Several broker terminals (Zerodha, Dhan, Upstox) display computed Greeks. For free, you can use the option chain at our NIFTY page alongside any Black-Scholes calculator.