What is a good IV rank?

There is no universal level. IV rank describes where today's implied volatility sits within this stock's own past year, so 50 is average for that name — not for the market. A high reading means options are expensive relative to that stock's own history.

Why did my option lose value when the stock moved the right way?

Implied volatility collapsing after an event can cost more than the move gained. It is the most common explanation for a correct direction with a losing option position, and it is invisible on an at-expiration payoff chart.

Is high implied volatility a signal in itself?

It is a price, so it is information about what the market expects, not a recommendation. It tells you what you are being paid for taking the other side of that expectation.

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Implied volatility and IV rank: what rich premium really means

Selling options looks best exactly when it is most dangerous, and implied volatility is the number that explains why.

Implied volatility is a price, not a prediction

The Black–Scholes formula takes an option's market price and returns the volatility that would make that price correct. That output is implied volatility: the annualised size of the move the market is currently charging for.

It is therefore a summary of what options cost rather than a forecast. Two stocks can have identical charts and very different implied volatilities, because the market is pricing the possibility of different future events rather than describing the past.

Higher IV means options cost more, for both buyers and sellers.
IV is quoted per expiry, so one stock has a whole curve of them, not one number.
IV changes when the market's expectation changes, which is why it collapses after events resolve.

IV rank and IV percentile are not the same thing

Both try to answer "is this high or low for this stock", and they answer it differently. IV rank compares the current implied volatility to the highest and lowest values over the past year and returns where it sits in that range. IV percentile returns the share of days in the past year that had lower implied volatility.

A stock whose IV has been pinned near its low all year can show a rising rank while its percentile is unremarkable, and vice versa. Quoting one while meaning the other is a common source of confusion in options commentary, including our own tool labels — the tool states which measure it is showing.

Why high IV pays more, and what you are being paid for

A short option in a high-IV name collects more premium for the same distance from the stock. That is not a market oversight: the pricing reflects a wider expected distribution, so the strike you sold is more likely to be reached than the same delta in a quieter name suggests, and gaps are larger when they come.

The uncomfortable part is the correlation. Implied volatility rises most in the situations where selling options is worst — a deteriorating stock, an unresolved event, a falling market. The premium is compensation for accepting that, and it is only an edge if the future distribution turns out narrower than the one you were paid for.

Where IV reasoning breaks down

High IV rank means expensive options, not an advantageous trade. It says nothing about direction, and a short strike chosen purely because the premium is rich can be a strike that is far more likely to be reached than it looked.

Implied volatility is also always looking at the same horizon as the option. Selling a 45-day option because IV rank is at the top of its range tells you nothing about the volatility over the next 45 days — which is the only window the position is exposed to.

Questions

What is a good IV rank?: There is no universal level. IV rank describes where today's implied volatility sits within this stock's own past year, so 50 is average for that name — not for the market. A high reading means options are expensive relative to that stock's own history.
Why did my option lose value when the stock moved the right way?: Implied volatility collapsing after an event can cost more than the move gained. It is the most common explanation for a correct direction with a losing option position, and it is invisible on an at-expiration payoff chart.
Is high implied volatility a signal in itself?: It is a price, so it is information about what the market expects, not a recommendation. It tells you what you are being paid for taking the other side of that expectation.