How vega works
Implied volatility (IV) is the market's estimate of how much the underlying will move, taken from option prices. When traders expect larger moves, they pay more for options, IV rises and every option's price rises with it. Vega measures each option's share of that change.
- Bought options have positive vega. They gain when IV rises and lose when it falls.
- Sold options have negative vega. They lose when IV rises and gain when it falls.
- At-the-money options have the highest vega, and vega is higher the longer the time to expiry.
- Vega falls as expiry nears, because there is less time for volatility to matter.
A worked example on one Nifty lot
Nifty is at 25,000 with 12 days to expiry. The at-the-money 25,000 call at different levels of implied volatility:
| Implied volatility | Call price | Change from 14% | On one lot of 65 |
|---|---|---|---|
| 12% | ₹244.50 | −₹36.00 | −₹2,340 |
| 14% | ₹280.50 | — | — |
| 16% | ₹316.50 | +₹36.00 | +₹2,340 |
| 20% | ₹388.60 | +₹108.10 | +₹7,027 |
Each point of IV is worth about ₹18 on this call, matching its vega of 18.00. A buyer who paid ₹280.50 at 14% IV loses ₹2,340 a lot if IV falls two points, before any move in Nifty. A seller gains the same.
Vega and time to expiry
| Days to expiry | 25,000 call price | Vega | Rupees per IV point, one lot |
|---|---|---|---|
| 30 | ₹469.35 | 28.26 | ₹1,837 |
| 12 | ₹280.50 | 18.00 | ₹1,170 |
| 5 | ₹174.70 | 11.65 | ₹757 |
| 1 | ₹75.35 | 5.22 | ₹339 |
A 30-day option moves more than five times as much per IV point as a 1-day option. Traders who want to trade volatility itself use longer expiries; traders who want to avoid IV risk use shorter ones, at the cost of faster time decay.
Vega after an event
Implied volatility rises before scheduled events such as the RBI policy, the Union Budget, US data or a company's results, and usually falls as soon as the event is over. A bought option can be right on direction and still lose if the fall in IV outweighs the move. On the 12-day call, a 100-point rise in Nifty is worth about ₹54 a unit by delta, but a 4-point fall in IV takes back about ₹72. The full effect is explained in implied volatility crush.
Vega and India VIX
India VIX is the implied volatility of near-term Nifty options, published by NSE. When VIX rises from 14 to 18, the vega of every Nifty option converts that rise into higher prices: about ₹72 on the 12-day at-the-money call, or ₹4,680 a lot. Option sellers watch VIX because a rising VIX raises both their losses and their margins; buyers watch it because a high VIX means options are expensive to buy.
Vega of a position
A position's vega is the sum of its legs' vegas, with the sign reversed for sold legs. A short straddle at 25,000 with 12 days left has a vega of about −36 a unit, or −₹2,340 a lot for each IV point. A bull call spread that buys the 25,000 call and sells the 25,200 call has a vega of 18.00 − 17.66 = 0.34, almost none: the sold leg cancels the bought leg's exposure to IV. That is why spreads are the usual way to trade a direction through an event.
When vega matters most
- Before events, when IV is high and likely to fall.
- Long-dated options, where vega is largest.
- Straddles and strangles, which are bets on volatility as much as on direction.
- Option selling when VIX is low, when a rise in IV can wipe out weeks of theta.
Related terms
- Delta meaning: how much an option moves per point of the underlying
- Theta meaning: what an option loses each day to time
- Gamma meaning: how fast delta changes
- Volatility meaning: realised and implied volatility defined
Learn more
- Option greeks: vega with the other Greeks on Nifty examples
- Implied volatility crush: what happens to options after an event
- Implied volatility calculator: the IV behind any option price
Frequently asked questions
What does a high vega mean?
That the option's price is very sensitive to changes in implied volatility. Long-dated at-the-money options have the highest vega.
Is vega the same as implied volatility?
No. Implied volatility is the market's estimate of future movement. Vega is how much an option's price changes when that estimate changes by one point.
Why does vega fall near expiry?
With little time left, a change in expected volatility has little time to affect the outcome, so the option's price responds less to it.
How do I reduce vega risk?
Use spreads, where the sold leg offsets the bought leg's vega, or trade shorter expiries, which have lower vega but faster time decay.
Where can I see vega?
In an option chain that shows Greeks, such as QuantPower's option trading app, and in the black scholes option pricing calculator.