Implied volatility: what it is and how it prices options

Written by the Tactfolio research teamPublished Data as of 6 min read

Implied volatility is how much the options market expects a stock to swing, worked out backward from option prices. It is shown as a yearly percent, such as 30%. When implied volatility is high, options cost more. It is a forecast built into prices. It does not record how much the stock actually moved.

Key points#

  • Implied volatility (IV) looks forward. Historical volatility looks back at real price moves.
  • Higher IV means bigger expected swings, so both calls and puts cost more.
  • IV often rises before known events, like earnings, and drops right after. Traders call the drop “IV crush”.
  • The VIX is a widely watched IV number. It tracks expected swings in the S&P 500.
  • IV says how big a move might be, not which way it will go.

Risk note. Options can expire worthless. Selling options can lose far more than the premium you collect.

What is implied volatility?#

Implied volatility is the size of future price swings that today’s option prices suggest. Option prices depend on a few inputs: the stock price, the strike, the time left, interest rates and expected swings. Everything except expected swings can be looked up. So traders take the market price of the option and solve for the swing that fits. That number is the implied volatility.

Volatility means how much a price moves up and down. It is usually stated as a yearly percent.

A rough rule helps you read it. An IV of 16% suggests typical daily moves of about 1%. An IV of 32% suggests about 2% a day. The rule comes from dividing the yearly number by 16, as explained in “The details” below.

If options are new to you, our put vs call guide covers the basics first.

Implied volatility vs historical volatility#

The two numbers answer different questions. One asks “how much might it move?” The other asks “how much did it move?”

Implied volatilityHistorical volatility
Comes fromOption prices todayPast daily price changes
LooksForwardBackward
Changes whenDemand for options changesNew prices come in
Typical useJudging if options look cheap or costlyMeasuring risk, sizing positions

Over long periods, index options have usually priced in a bit more volatility than the market later delivered, according to Cboe. That gap is one reason some traders sell options. It is not free money. The gap can flip hard in a crash.

What is the VIX?#

The VIX is an index of implied volatility for the S&P 500. Cboe describes it as a leading measure of the market’s expected near-term volatility, taken from S&P 500 option prices. Cboe introduced it in 1993.

The VIX is quoted in points that read like a yearly percent. A VIX of 20 means option prices expect the S&P 500 to swing at a pace of about 20% a year. That forecast covers the next 30 days. A higher VIX usually comes with falling or nervous markets. People often call it the “fear gauge”.

What is IV crush?#

IV crush is a sharp drop in implied volatility after the event traders were waiting for has passed. It often happens the day after earnings.

Example with round numbers. Say a stock trades at $100 and reports earnings tomorrow. A call with a $100 strike costs $5.00 per share. Its IV is 60%, because traders expect a big move. Its delta is 0.50 and its vega is 0.10.

The next day the stock rises to $102. You were right about the direction. But the news is out, and IV falls to 30%.

  • The $2 rise adds about $1.00 (delta 0.50 × $2).
  • The 30-point drop in IV takes away about $3.00 (vega 0.10 × 30).
  • One day of time decay takes a little more.

The call is now worth roughly $2.90. You were right on direction and still lost over 40%. That is IV crush. These are rough estimates from the Greeks, and real prices can differ.

How implied volatility affects option prices#

Higher IV raises the price of both calls and puts. A wider range of likely outcomes gives the option more chance to end up worth something.

Vega measures this. It is how much an option’s price changes for a 1 point move in IV. The Options Industry Council gives an example: an option worth $4 with a vega of 0.15 would gain about $0.30 if IV rose 2 points. Our guide to the options Greeks covers vega next to delta, gamma, theta and rho.

IV also feeds into time decay. The Options Industry Council notes that higher IV usually means a larger theta, because there is more time value to lose.

Common mistakes#

  • Buying options right before earnings without checking IV. You can be right on direction and still lose to IV crush.
  • Thinking high IV means the stock will fall. IV measures size, not direction.
  • Selling options because IV “looks high”. IV can go higher. Selling options can lose far more than the premium.
  • Comparing IV across very different stocks. A utility stock and a young tech stock have very different normal levels. Compare a stock’s IV with its own past.
  • Treating the VIX as a timing tool. A high VIX tells you the market is nervous. It does not tell you when the nerves will pass.

Try it on Tactfolio#

Tactfolio does not trade or backtest options, so you cannot test IV trades here. You can test volatility ideas with stocks and funds. The volatility-managed portfolio holds less of the S&P 500 after jumpy months and more after calm ones, using historical volatility. As of September 25, 2026, its hypothetical backtest from mid-2007 returned about 7.5% a year, against about 11% for the S&P 500. Its worst fall was about 17%, against 55%. It also lagged in rebounds, gaining 8% in 2009 while the S&P 500 gained 26%. In the strategy builder, conditions can also read the VIX level, as the builder reference shows.

Common questions#

What is a good implied volatility for options?#

There is no single good level. IV is high or low only next to that stock’s own past. Many traders compare today’s IV with its range over the past year.

Is high implied volatility good or bad?#

It depends on your side of the trade. High IV makes options cost more, which hurts buyers and pays sellers more premium. But high IV also means the market expects big moves, which raises the risk for sellers.

How is implied volatility calculated?#

It is solved backward from an option’s market price using a pricing model. Traders put in the stock price, strike, time left and interest rate, then find the volatility that makes the model match the market price. Your broker does this for you.

Why does implied volatility drop after earnings?#

Before earnings, no one knows the news, so traders pay up for options. Once the news is out, that unknown is gone. IV falls back toward normal, often in a single day.

Is the VIX the same as implied volatility?#

The VIX is one kind of implied volatility. It covers the S&P 500 index as a whole, worked out from many index options. Single stocks have their own IV.

The details#

  • IV is quoted as an annualized standard deviation of returns. A standard deviation is a measure of how far values usually stray from their average.
  • To turn yearly IV into a typical daily move, divide by the square root of about 252 trading days, which is close to 16. To get a typical monthly move, divide by the square root of 12, about 3.5.
  • A “typical” move here means one standard deviation. Under the usual model, prices stay inside it about two thirds of the time. Real markets have more big days than that model expects.
  • Tactfolio’s volatility reading in the builder is historical: the annualized volatility of daily returns over a window you choose.
  • The volatility-managed portfolio comes from Alan Moreira and Tyler Muir’s paper Volatility-Managed Portfolios in the Journal of Finance (2017). Tactfolio tests the paper’s no-leverage version.

Sources

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