Vega: The Greek That Pays When Fear Arrives
Vega measures how much an option is worth when expectations about future movement change, independent of the price going anywhere.
The Input Nobody Can Observe
Every input to an option price is knowable except one. The current price, the strike, the time remaining, and the interest rate are all facts you can look up. Expected future volatility is not. It has to be assumed.
Because it is the only unobservable input, it is also the one that moves for reasons that have nothing to do with the underlying asset. Vega measures how much the option value changes when that assumption changes by one percentage point.
An option with a vega of 0.12 gains about 12 cents if implied volatility rises from 20 to 21, with the stock price untouched.
Both Sides Gain
Calls and puts both have positive vega. Higher expected movement makes every option more valuable, because more movement means a greater chance of finishing well in the money, and the downside is capped at the premium either way.
This is the asymmetry at the centre of options. The buyer keeps the entire upside of a large move and loses only what was paid. More uncertainty is therefore worth more, regardless of direction.
A long option position is a position on uncertainty itself. Direction is the second bet, layered on top.
Where Vega Lives
Vega is largest for at the money options with long time remaining. Time is what gives volatility room to matter. A change in the assumed rate of movement compounds over months and barely registers over hours.
A two year option has substantial vega and almost no gamma. A contract expiring tomorrow is the reverse: enormous gamma, negligible vega. Long dated positions are trades on the volatility level. Short dated ones are trades on movement actually happening.
| Time to expiry | Vega | Gamma |
|---|---|---|
| 2 years | High | Low |
| 3 months | Moderate | Moderate |
| 1 day | Near zero | Extreme |
Why the Right Call Still Loses
The common version of this runs through earnings. Implied volatility rises into the announcement because the outcome is uncertain and known to be uncertain. A trader buys calls, the company beats expectations, the stock rises, and the calls are worth less than they were the day before.
What happened is a volatility crush. The uncertainty that justified the elevated implied volatility resolved. The vega loss overwhelmed the delta gain. The directional view was correct and the trade still lost, because the price paid already contained the expected move.
Volatility as an Asset
Vega is what makes volatility tradeable on its own. A trader who believes the market is underpricing future turbulence can construct a position with minimal delta and substantial positive vega, expressing a view on the level of fear rather than on the direction of anything.
The same logic drives the demand for index options from institutions. They are not forecasting a crash. They are buying an asset that appreciates when correlations rise and everything falls together, which is exactly when the rest of the portfolio needs help.
The Asymmetry of the Short Side
Selling vega collects premium in calm conditions, and calm conditions dominate the calendar. The problem is the shape of the loss. Volatility can double or triple in days, and the seller carries that exposure at whatever size the quiet period encouraged them to build.
February 2018 made this concrete for products designed to short volatility. Several lost most of their value in a single session. Nothing about the underlying index moved that far. The volatility input did.
The Bottom Line
Vega prices the one input to an option that cannot be observed, which makes it the channel through which sentiment enters the market. It explains why a correct directional call can lose money after earnings and why insurance gets expensive exactly when everyone wants it. Trading options without watching vega means holding a position on fear without knowing it.