Vega of the at the money call is highest with the most time left and falls toward expiry
Two options with the same strike and expiry are priced from the same index level, and what moves their price between dates is the volatility the market expects. When that expectation rises, both the call and the put cost more, because the chance of a large move in either direction is higher. Vega is that sensitivity: the rupee change in the premium of one lot for each one point rise in implied volatility.
The chart shows vega for the at the money call on the 10 Jun 2026 chain. With twenty days left, vega is at its largest. As the days run down the curve falls, because there is less time for a move to matter. At expiry the option is worth only its intrinsic value, and vega is close to zero.
Vega explains why an option can gain on a day the index is flat. If implied volatility rises a few points and the index stays where it is, the premium still rises. The reverse is what happens after a known event. The index may move as expected, but the volatility priced in falls, and the premium falls with it. That fall is covered in the question on IV crush.
Vega is a rupee figure per lot per vol point, so it scales with the lot size and with the level of implied volatility. A short option has negative vega, so it loses when volatility rises. That is why a short option can lose on a day the index barely moves.
The vega in the chart is a Black 76 figure, and it changes with every input. It describes the model, not a forecast.
Before you trade. Derivatives trading carries a high risk of loss. SEBI's study "Profitability of Individual Traders in the Equity Derivatives Segment (FY25 to FY26)" (August 2026) found that 87.7% of individual traders in equity F&O made net losses in FY26, with aggregate net losses of Rs 91,685 crore. Read the SEBI study