The last three lessons covered how an option's price reacts to the underlying moving (delta), to time passing (theta), and to delta's own sensitivity (gamma). Vega covers a different input entirely: how much an option's price changes when the market's expectation of future volatility changes, even if the underlying itself hasn't moved at all.
Vega is quoted as the change in an option's price for a 1 percentage point change in implied volatility (IV). An option with a vega of 0.10 would be expected to gain about $0.10 in value, or $10 per contract, if IV rises by one percentage point, and lose roughly the same if IV falls by one point.
What implied volatility actually is
Implied volatility is easy to misread as a prediction. It isn't one. IV is the market's current estimate, baked into an option's price, of how much the underlying might move over the life of that option. It's derived from the price itself, working backwards through an option pricing model, rather than measured directly. Higher IV means the market is pricing in a wider range of possible outcomes; lower IV means it's pricing in a calmer, narrower range. Either way, it's a forecast embedded in a price, not a guarantee of what will actually happen.
What high and low IV mean for a trade
Because vega links option prices to IV, the level of IV directly affects how expensive options are. High IV means richer premiums: more for a seller to collect, but also a market that's pricing in a bigger expected move, which usually means wider expected price swings to manage. Low IV means cheaper premiums and, generally, a market pricing in calmer conditions. Neither is inherently good or bad; it's context that changes how a given strike or spread should be sized and read.
IV around scheduled events
IV often rises heading into a known event on the calendar, an earnings announcement being the clearest example, something covered in more detail later in this curriculum. The market prices in extra uncertainty ahead of the event because a genuinely uncertain, binary outcome is coming. Once the event passes and that uncertainty resolves, IV frequently drops sharply, sometimes called "IV crush." That pattern will come up again in a later module in more practical detail, but it's worth knowing the term and the shape of it now.
What this doesn't mean
- It doesn't mean high IV guarantees a big move, or that low IV guarantees a quiet one. IV is a market estimate, not a forecast that always plays out.
- It doesn't mean vega acts alone. In a live market, delta, theta, gamma and vega are all moving the price at once, not one at a time in isolation.
- It doesn't mean IV crush happens on every event. It's a common pattern around scheduled announcements, not a rule that applies to every single one.