Introductory Context
"Vega measures how much an option's premium changes per 1 percentage point change in implied volatility. Always positive for long options. ATM options have highest vega. Longer-dated options have higher vega. Vega is the primary sensitivity for event traders — it determines IV expansion capture and IV crush exposure."
The Precise Definition
Vega = Change in option premium ÷ Change in IV (per 1 percentage point). For a Nifty ATM call with vega ₹6 per unit: if India VIX rises from 14% to 15% (1 percentage point), the call gains ₹6 per unit. If VIX rises from 14% to 20% (6 percentage points), the call gains ₹6 × 6 = ₹36 per unit — even with zero Nifty movement. If VIX falls from 20% to 14% (IV crush of 6 points), the call loses ₹36 per unit.
On 1 lot (75 units): a 6-point VIX rise generates ₹36 × 75 = ₹2,700 gain purely from vega. A 6-point VIX fall (post-event crush) generates ₹2,700 loss purely from vega. These vega-driven P&L swings occur regardless of any Nifty directional move — they represent pure volatility sensitivity.
Vega Sign Conventions
Long call: positive vega (benefits from IV rise). Long put: positive vega (benefits from IV rise). Short call: negative vega (hurt by IV rise). Short put: negative vega (hurt by IV rise). All long options benefit from rising IV. All short options are hurt by rising IV. This symmetric vega behaviour for all long options means: any bought option is a bet that IV will not fall significantly while you hold it.
Vega Across Strikes and Expiries
Vega Peaks at ATM
Like gamma, vega is highest for ATM options and falls on both sides toward deep ITM and deep OTM. ATM options have maximum uncertainty about their final state — and this uncertainty is most sensitive to IV changes. Deep ITM options are almost certain to expire ITM regardless of volatility level; deep OTM options are almost certain to expire OTM regardless. ATM options are the most 'on the fence' and therefore most affected by changes in the market's volatility estimate.
Vega Increases With Time to Expiry
A 30-day ATM Nifty option has higher vega than a 7-day ATM option at the same strike. This is because a longer-dated option has more time for volatility changes to compound — more uncertainty remains unresolved. Monthly options typically have 3–4× the vega of weekly options at the same strike, making them much more sensitive to VIX changes.
Weekly ATM Nifty option (7 days): vega ≈ ₹3–₹5 per unit
Monthly ATM Nifty option (25 days): vega ≈ ₹8–₹12 per unit
Quarterly option (90 days): vega ≈ ₹16–₹22 per unit
Vega for Event Trading
The higher vega of monthly options makes them more appropriate for capturing pre-event IV expansion. A weekly option bought 5 days before the Budget gains less from VIX rising from 14 to 20 (6-point VIX increase × ₹4 vega = ₹24/unit) than a monthly option (same 6-point increase × ₹10 vega = ₹60/unit). For pure IV expansion plays, longer-dated options provide more vega bang for the premium spent.
Vega and the IV Crush Calculation
Before any options purchase ahead of an event, calculate vega exposure explicitly:
Vega loss from expected IV crush = vega × expected IV decline (in percentage points)
Example: ATM Nifty call bought at VIX 20%, vega ₹6/unit. Expected post-Budget VIX: 12% (decline of 8 points). Vega loss = ₹6 × 8 = ₹48/unit. On 2 lots: ₹48 × 75 × 2 = ₹7,200 vega loss regardless of direction. To break even after IV crush, delta must generate ₹48/unit: required Nifty move = ₹48 ÷ delta = ₹48 ÷ 0.50 = 96 points minimum just to offset IV crush.
Vega in Portfolio Management
Net portfolio vega = sum of vega contributions across all positions. Long options: positive vega. Short options: negative vega. A portfolio with net positive vega benefits from rising VIX (pre-event IV expansion). A portfolio with net negative vega benefits from falling VIX (post-event IV normalisation).
Long call + long put (straddle): very positive vega — maximum IV sensitivity
Short straddle: very negative vega — benefits when IV falls
Bull call spread: low net vega (long and short legs partially cancel)
Iron condor: negative net vega — benefits from IV compression
Vega is the options market's version of a fear barometer embedded in your position. When you buy options, you become long fear — you benefit when the market becomes more afraid. When you sell options, you become short fear — you benefit when the market becomes calmer. Every position takes a stance on volatility. Knowing your vega makes that stance explicit rather than accidental.