Vega is an option greek representing the theoretical price change in an option for a corresponding 1% change in implied volatility.
At the money options are most sensitive to changes in vega, and ATM strikes therefore have the highest vega. This is because corresponding price changes can easily drive those options ITM or OTM. Vega will also be higher with greater time remaining to expiration, as there is more time for volatility to change during the life of the option.
Vega is closely tied to implied volatility, which makes it the central aspect of a discussion of an option’s vega.
Short calls and short puts have a negative vega because they will benefit from contracting IV. This is because lower IV points to less expected movement in the price of the underlying, decreasing the likelihood of a big change in option prices.
Alternately, long calls and long puts have a positive vega, which means they will benefit from expanding IV. An expansion in IV is an increased expectation of wider price fluctuations in the underlying, which will in turn increase option premiums.
Therefore, increased IV increases option premiums, whereas decreased IV decreases option premiums.
An option position with negative vega will lose value as IV increases. An option position with positive vega will gain value as IV increases.
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