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What is an option's vega, in plain words?

Vega is the change in an option's price for a one-point change in implied volatility 1. It is highest when the stock is near the strike and shrinks as expiry approaches 1. Along with time passing 2, it is why an option can gain or lose value while the stock stands still. By the formula, an option you bought has a positive vega and one you sold a negative one 3.

A $50 stock and a call with a $50 strike, priced at 30% implied volatility (made-up numbers). Change the implied volatility and the days left.

Source: the StrikePath engine, pricing with the Black–Scholes formula 3 at 4.3% interest a year; a simulated example, not market prices. For learning; not advice.

Vega in numbers

With 30 days left, the call above costs $1.80 at 30% implied volatility and has a vega of about 6 cents by the formula 3. At 35% it costs $2.09: five points added about 29 cents a share, $29 a contract, with the stock unchanged.

Where vega matters

Implied volatility tends to rise before a company reports and fall after 4, and option prices can fall sharply with it 5. Vega is how much of that reaches one option's price. More time left means more vega 1: move the days to see it.

What this shows, and what it doesn't

The formula's vega for one strike. In real markets implied volatility moves differently at different strikes and expiries 6, so one number is a starting point, not the whole picture.

Go further

What is implied volatility? →The swing a price assumes.What is IV crush? →Vega after earnings.
Sources (6), checked 20 October 2026 and 27 October 2026
  1. CME Group, “Options Vega – The Greeks” (Option Greeks course). Read it (read 27 October 2026)
  2. The Options Industry Council, “Theta”. Read it (read 20 October 2026)
  3. Fischer Black and Myron Scholes, “The Pricing of Options and Corporate Liabilities”, Journal of Political Economy 81(3), 637–654, 1973. Read it (read 20 October 2026)
  4. Andrew Dubinsky and Michael Johannes, “Earnings Announcements and Equity Options”, working paper, Columbia Business School, citing Patell and Wolfson (1979, 1981). Read it (read 20 October 2026)
  5. The Options Industry Council, “Implied Volatility and the IV Crush” (video). Read it (read 20 October 2026)
  6. CME Group, “Implied Volatility”. Read it (read 20 October 2026)

Now try it on a scenario of your own

Pick where a simulated stock might be, and by when: drag one dot and see, side by side, what buying shares, one option, or a pair of options (a call or put spread) would each do. Free, no sign-up.

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