What is vega risk?
In one line: Vega risk is the effect of a change in implied volatility on an option's price; when IV rises a short option loses value for the seller, and when IV falls it gains.
How it works
Vega is the amount an option's price changes when Implied volatility moves by one point. If vega is 0.05 and IV goes from 30% to 31%, the option's price rises about $0.05 per share, or $5 per contract.
Vega risk is that effect working against you. When you sell an option, you want its price to fall. Rising IV pushes it up, even if the stock hasn't moved. Falling IV pulls it down, which is a gain for you.
IV usually rises when the market gets nervous: a sell-off, bad news, an earnings date coming up. It usually falls when the fear passes. So a short option often loses money on a scary day for two reasons at once: the stock dropped, and IV jumped.
Longer-dated options have more vega. A 60-day put reacts more to an IV change than a 14-day put. In the wheel strategy, that's part of why sellers often stay around 30 to 45 days.
An example (hypothetical)
An illustration, not a trade idea. Made-up stock XYZ trades at $50. You sell a 45-day Put option at the $45 Strike price for $1.00 when IV is 30%. Vega is about 0.06.
| What happens | IV | XYZ | Put price (about) | Your position on the put |
|---|---|---|---|---|
| Quiet week, IV eases | 25% | $50 | $0.70 | +$30 |
| Market scare, stock flat | 40% | $50 | $1.60 | −$60 |
| Scare plus a drop | 40% | $47 | $2.60 | −$160 |
| Weeks later, fear fades, stock recovers | 28% | $50 | $0.60 | +$40 |
In the second row the stock didn't move at all. The put still went against you by $60, purely because IV rose. The third row is the usual pair: the stock falls and fear rises together.
Why it matters for sellers
Vega risk is why "the stock didn't move, so why am I losing?" is a common question. It also explains the two moments sellers care about most:
- Selling into high IV. A premium is fat because IV is high. If IV then falls, the option's price falls with it, which is the gain. If IV keeps rising, the premium looked fat for a reason.
- Earnings. IV climbs before the report and usually collapses after. Sellers call the drop "IV crush". It helps a short option, but the stock's gap on the news can swamp it. See our IV crush guide.
A useful check before selling: look at IV rank or IV percentile. Selling when IV is low leaves little room for it to fall and plenty of room for it to rise. That's vega risk tilted against you.
Questions
Is vega good or bad for option sellers?
Falling IV is good for a seller, rising IV is bad. Since fear tends to rise fast and fade slowly, the bad days can be sharp. Sizing so a jump in IV is survivable matters more than predicting it.
Why did my short put lose money when the stock went up?
Implied volatility probably rose. If a big event is coming, IV can climb even on a green day, lifting the option's price. Check the option's IV on the day you sold versus today.
Which options have the most vega risk?
Longer-dated options and at-the-money options. A 90-day put reacts far more to an IV change than a 10-day put at the same strike.
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