Why option prices jump before RBI policy and crash after — and how Vega measures the size of that move. With current NIFTY ATM Vega and IV.
Vega measures how much an option's price changes when implied volatility (IV) moves 1 percentage point. An option with Vega ₹15 gains ₹15 if IV rises from 14% to 15%, all else equal.
Vega is the Greek that explains why options get expensive before events like RBI policy or US Fed announcements, then collapse after — even when the underlying barely moved. This 'IV crush' pattern is one of the most reliable edges in options trading when you know which side of it to be on.
Vega is highest at the at-the-money strike and on the longest-dated expiry. A monthly NIFTY option has 4-8x the Vega of the same-strike weekly because there's more time for IV to play out.
Practical implication: if you're betting on IV regime changes (rather than direction), trade monthly options. The Vega exposure is much cleaner.
Far-OTM options have very low Vega — they're already priced as 'unlikely to be ITM' so IV changes don't move them much.
IV expansion happens in the run-up to known catalysts. RBI policy meetings, US Fed announcements, election results, major Q4 earnings — IV ramps up 30-50% in the days before. Option premiums get rich. Long Vega positions (long straddles, long calendars) profit if you bought before the expansion.
IV crush happens after the event. Whatever the underlying moved, IV typically drops sharply back to pre-event levels. Long premium positions get hurt; short premium positions benefit.
The classic trade: buy a long straddle 5-7 days before an event when IV is normal, sell it the morning after the event (BEFORE IV crushes too far). The directional move can be modest — the IV expansion alone usually pays for the trade.
The mirror trade: sell premium AFTER the event when IV has crashed and you don't expect another catalyst before expiry. Iron condors, short strangles, and short straddles benefit from low and stable IV — exactly the regime that follows event-day crush.
But beware: if IV looks 'cheap' it might be cheap because the next event is coming. Don't sell premium into RBI week unless you have strong conviction that IV is still mispriced.
Strota's option chain shows current IV alongside historical IV percentiles — so you can see whether 'current IV is in the 20th percentile of the last 90 days' before committing to a short premium position.
Compare today's IV to its 90-day or 180-day percentile distribution. Below the 20th percentile = cheap (favours buying premium). Above the 80th percentile = expensive (favours selling premium). The Strota option chain page shows both current IV and the recent percentile range.
Usually 12-18% during quiet periods, 18-25% in volatile regimes, and can spike to 30%+ around major events. BANK NIFTY IV is typically 30-50% higher than NIFTY IV across all regimes.
Yes but less than for monthlies. Weekly options have shorter time-to-expiry so there's less room for IV to play out. Most of a weekly's Vega risk is concentrated around immediate events (e.g. tomorrow's Fed announcement). For genuine IV-regime trades, use monthlies.
Mathematically no (would mean zero expected movement). Practically, IV rarely drops below 8-10% even in dead-quiet markets. The lower bound is set by realised volatility — IV can't crash much below what the underlying actually does.
Vega is sensitivity to IV. Vomma is sensitivity of Vega itself to IV changes — i.e. how Vega evolves as IV moves. For retail traders, Vega is enough; Vomma matters mostly for institutional volatility traders.