Vega — Volatility Exposure Beyond Direction
Why vega is not constant and what makes it expand
A trader holds a long 30-day at-the-money call on a $200 stock, bought when implied volatility was 25%. Overnight, a Federal Reserve speech reignites uncertainty about the path of rates. The stock barely moves at the open — up sixteen cents.
Implied volatility on the same call jumps from 25% to 32%. The trader's screen shows the call's value rising by roughly $1.60 per share before the underlying has done anything meaningful at all.
The position is not benefiting from a directional move; the entire P&L is coming from the seven-point expansion in implied volatility multiplied by the option's vega. Vega is the Greek that quantifies exactly how much of an option's price change comes from changes in implied volatility, separate from any underlying movement. Of the five canonical Greeks, vega is structurally distinct: Delta, Gamma, Theta, and Rho all measure sensitivity to inputs that are externally observed and directly traded (stock price, time, interest rate).
That is the opening. Finishing a lesson is where it stops being interesting and starts being useful: the full lesson runs to 9 sections and ends with 6 practice questions. A free account is what opens the rest, and the other 255 lessons in the Academy with it. No card.
What this lesson covers
- 1Vega is largest at-the-money and concentrated near the spot
- 2Vega is approximately constant in vol level — for at-the-money options
- 3Vega Surface Explorer
- 4Vega in closed form (BSM)
- 5Vega vs moneyness for a 30-day call ($200 strike, $200 stock, 30% IV, 4.5% rate)
- 6Vega scaling with time — same ATM call across expirations ($200/$200, 30% IV, 4.5% r)
- 7March 2020 — when SPX implied vol tripled in three weeks and vega exposure rewrote book P&Ls
- 8Where to see this on the platform
- 9Summary