Options & Derivatives
Implied Volatility Explained: IV, IV Rank and the Earnings Crush
IV is solved backwards out of the option price rather than measured from history. Here is the arithmetic that turns a percentage into an expected dollar move.
What volatility number would make this price correct? That is the entire question implied volatility answers. The stock price, the strike, the days remaining and the interest rate are all observable, so implied volatility is the leftover input you solve for, which makes it a statement about what the market expects of the stretch between now and expiry, and nothing that has already happened goes into it.
Solved backwards out of the price
Historical volatility comes from the stock’s own past returns. It is also called realized volatility. Take the standard deviation of daily moves and annualize it. The whole calculation sits on data that already exists, so anyone with a spreadsheet and a price history can run it.
Implied volatility runs the other way. Take the quoted premium, hold everything else fixed, and solve for the volatility input that reproduces that exact price, and the answer arrives annualized and expressed as a percentage.
The gap between the two carries the information. A stock whose shares have moved 22% annualized over the past year, with options priced at 38% implied, is telling you the market expects the next stretch to be rougher than the last one. Whether the market is right about that is a separate question. It is also a much harder one.
From a percentage to a dollar range
The quoted figure is annualized. Scaling it to your holding period takes a square root.
1 standard deviation move = stock price x IV x sqrt(days / 365)
Stock at $100, implied volatility 30%, 42 days to expiry:
$100 x 0.30 x sqrt(42 / 365) = $100 x 0.30 x 0.339 = $10.17
The options are priced for roughly a $10.20 move over six weeks in either direction. Under the model’s assumptions about two thirds of outcomes fall inside that band.
| Implied volatility | 1 SD over 42 days | Range around $100 |
|---|---|---|
| 15% | $5.09 | $94.91 to $105.09 |
| 30% | $10.17 | $89.83 to $110.17 |
| 45% | $15.26 | $84.74 to $115.26 |
| 80% | $27.13 | $72.87 to $127.13 |
The daily version, and the sanity check nobody runs
daily expected move = stock price x IV / sqrt(252) = $100 x 0.30 / 15.87 = $1.89
That uses trading days, because trading days are when prices change. Now compare $1.89 against the chart. A stock priced at 30% implied volatility that has been shuffling $0.60 a day is being charged for a range it has stopped producing. The comparison takes thirty seconds. Nothing else on this page is more useful.
IV rank and IV percentile
A reading of 30% means nothing by itself. A regulated utility at 30% is having an unusual month. A small biotechnology name at 30% is asleep. Both measures below fix that. They put the number back into the context of the same stock’s own history.
IV rank = (current IV - 52 week low) / (52 week high - 52 week low) x 100
Current IV of 30%, a 52 week low of 18% and a high of 62%:
(30 - 18) / (62 - 18) x 100 = 12 / 44 x 100 = 27.3
A rank of 27 puts today in the lower third of the past year’s range.
IV percentile asks a different question, counting the share of the past year’s sessions on which
implied volatility was lower than it is now, so if 103 of 252 sessions were lower, the percentile
is 103 / 252 = 41%. Percentile ignores the magnitude of the extremes, so a single panic day that
spiked IV to 62% wrecks the rank calculation and barely touches the percentile.
| Measure | Reading | What it says |
|---|---|---|
| IV | 30% | Options priced for a $10.17 move over 42 days |
| IV rank | 27 | Low within the past year’s range |
| IV percentile | 41% | Lower than today on 41% of the past year’s sessions |
Sellers want both numbers high. They are selling something priced richly against its own history. Buyers want the reverse. Neither reading says anything about direction. Any service that implies otherwise is selling you something.
Term structure
Implied volatility is quoted one number per expiry, and the expiries disagree.
| Expiry | Implied volatility | What it reflects |
|---|---|---|
| This week, earnings inside | 80% | One known event dominating a short window |
| Next month | 45% | The same event diluted across more days |
| Three months | 33% | Closer to the stock’s resting level |
A front month priced far above the later months is backwardation in the term structure, and it usually points at a dated event you can find on a calendar. The reverse shape, later months higher, is the normal resting state.
Skew
Within a single expiry, strikes disagree. In index options, downside puts consistently carry higher implied volatility than equidistant upside calls, because demand for crash protection never really stops and the people writing it want paying. That asymmetry is why a put spread and a call spread of identical width rarely cost the same amount, and it is a standing correction to the textbook assumption of one volatility per stock. The index version of the same phenomenon is in volatility and the VIX.
The earnings crush, worked
Stock at $100, earnings after tomorrow’s close, seven days to expiry. The at the money straddle, the $100 call plus the $100 put, prices off 80% implied volatility: the call is $4.45, the put is $4.35, the straddle costs $8.80, which is $880 for one of each.
That price is itself a forecast. The market is implying an earnings move of about
$8.80 / $100 = 8.8%. Many traders discount the straddle to around 85% of its price for a
cleaner estimate, giving 0.85 x $8.80 = $7.48, and I treat that adjustment as folklore with a
plausible mechanism behind it and no calibration I have ever seen.
The report lands. Implied volatility falls from 80% to 40% and one day passes.
| Scenario after earnings | Stock | Straddle | P/L on $880 |
|---|---|---|---|
| No move | $100.00 | about $410 | -$470 |
| Small move up | $104.00 | about $475 | -$405 |
| Move matches the implied | $108.80 | about $900 | +$20 |
| Large move down | $88.00 | about $1,215 | +$335 |
Look at the third row for a while. The stock moved 8.8%, exactly what was priced. The position made $20. Buying a straddle into earnings is a bet that the move beats the one already paid for, and being right about the direction contributes nothing at all.
Letting the reading choose the structure
The level should decide which structure you pick, and that is a bigger decision than whether to trade at all.
High against the stock’s own range favours selling structures where the premium works for you: covered calls, cash-secured puts, credit vertical spreads, or an iron condor when both wings need defining.
Low against the range makes premium cheap for the same exposure. That favours debit spreads and long calendars. Vega decides how much any of this matters. That number comes from the option Greeks.
Where this analysis fails
The model generating implied volatility assumes lognormal returns and constant volatility. Both assumptions break in precisely the conditions you care about most. Markets gap, gaps are far more frequent than the model allows, and skew exists largely because traders have priced in that the model is wrong.
A low IV rank also has a long history of staying low for months right up until it does not, and selling premium because rank is high carries no edge on its own, since rank is high exactly when something genuinely uncertain is approaching. The reading tells you what has been priced. Whether that price is fair is a judgement the number cannot make on your behalf, and I have yet to see a screen that admits this.
Next: the option Greeks for how vega converts a volatility change into dollars, and iron condors and strangles for the structures built specifically to sell what is described here. The options fundamentals quiz covers the vocabulary.
Frequently asked questions
What is implied volatility in simple terms?
Implied volatility is the annualized percentage move that the option price is consistent with, once you feed the price into a pricing model and solve backwards for the volatility input. It is the market's collective estimate of how far the stock travels between now and expiry. It says nothing whatsoever about direction.
How do I convert implied volatility into an expected move?
Multiply the stock price by the implied volatility, then by the square root of days to expiry divided by 365. A $100 stock at 30 percent implied volatility with 42 days left gives about $10.20, which is a one standard deviation move. Under the model's assumptions roughly two thirds of outcomes land inside one standard deviation.
What is IV rank and how is it different from IV percentile?
IV rank places the current reading between the 52 week low and high, so an IV of 30 with a range of 18 to 62 gives a rank of about 27. IV percentile counts the share of trading days over the past year when implied volatility was lower than it is now. One extreme day can distort rank badly while leaving percentile almost untouched.
Why does implied volatility fall after earnings?
Before the announcement the option price carries the uncertainty of an unknown result, so implied volatility is elevated. Once the numbers are public that uncertainty is resolved and the extra premium has nothing left to pay for. Implied volatility drops back toward its normal level within minutes of the release, which is what traders call the crush.
Does high implied volatility mean an option is expensive?
It means the option is expensive relative to the stock's own history, which is a useful comparison and an incomplete one. Implied volatility is often high because a real event is coming, so the premium can be a fair price for a genuinely wider range of outcomes. Compare the reading to the same stock's own range before calling anything expensive.
What is the volatility skew?
Skew is the pattern of different implied volatilities across strikes within one expiry. In equity index options, downside puts usually carry higher implied volatility than equidistant upside calls, because demand for crash protection is persistent and supply is not. A flat skew and a steep skew price the same range very differently.