Vega
What is Vega?
Vega estimates how much an option's value changes for a specified change in implied volatility, holding the underlying and other model inputs constant.
Vega is a local sensitivity to the model's implied-volatility input, not a complete measure of volatility risk. Surface shape, vol-of-vol, jumps, correlation, and liquidity can create losses even when aggregate vega is small. Reports should distinguish exposure by expiry and strike, use full surface scenarios, and explicitly disclose standardized measurement units so a decimal shock is not mistaken for a percentage-point shock.
How vega behaves
Long standard options generally have positive vega and short options negative vega. Vega is often larger for longer maturities and near-the-money options, but the surface and contract features matter. Market convention commonly reports change for one volatility point, though systems can use decimals or other scaling, making unit verification essential.
Example
An option has vega $0.12 per share per volatility point and multiplier 100. A rise from 20% to 21% IV suggests about $12 gain, all else equal. A rise from 20% to 25% is too large to assume perfect linearity, and underlying, skew, and time likely change simultaneously.
Surface exposure
A portfolio is not exposed to one universal IV. Each strike and expiry can move differently, creating skew, term-structure, and convexity risk. Aggregate vega can appear neutral while holding large offsetting exposures in short and long maturities. Event volatility can collapse after an announcement even when longer-dated volatility barely changes.
Vega versus realized volatility
Long vega benefits from higher marked IV, not automatically from high realized movement. Dynamic hedging links option profit to realized paths, implied price, gamma, and costs. Selling high IV can lose during jumps, while buying low IV can lose through decay. Historical averages do not establish fair compensation for current tail risk.
Practical checklist
Confirm unit, sign, multiplier, model, strike, expiry, and surface snapshot. Map vega by tenor and moneyness, stress parallel and nonparallel changes, and include underlying jumps and liquidity. Distinguish mark-to-market IV exposure from realized-volatility strategies. Do not aggregate incompatible volatility points or describe a vega-neutral portfolio as free of volatility, skew, or tail risk.
Sources and further reading
- Investor Bulletin: An Introduction to Options, Investor.gov, U.S. Securities and Exchange Commission