The IV Rank (Green line) is then calculated by looking at the high and low volatility over the number of days back specified in the input parameter, default is 252 (trading days in 1 year) and then calculating the rank of the current IV compared to the High and Low. This is not as reliable as the IV Percentile as the and extreme high or low could have a side effect on the ranking but it is included for those that want to use.
The IV Percentile is calculated by counting the number of days below the current IV, then returns this as a % of the days back in the input
You can adjust the number of days back to check the IV Rank & IV Percentile if you are not wanting to look back a whole year.
This will only work on Daily or higher timeframe charts.
In true TradingView spirit, the author of this script has published it open-source, so traders can understand and verify it. Cheers to the author! You may use it for free, but reuse of this code in a publication is governed by House Rules. You can favorite it to use it on a chart.