What is the difference between IV and HV?
Historical volatility (HV) is how much the price actually moved, worked out from its daily closes and written as a yearly percentage. Implied volatility (IV) is the move that option prices assume from now to expiry. HV looks back; IV looks ahead.
What is IV percentile and how is it different from IV rank?
IV percentile is the share of past days (here, up to a year) when IV was lower than today. IV rank is where today's IV sits between the period's lowest and highest: 0 at the low, 100 at the high. One spike can keep IV rank low for months, so the percentile is usually the steadier reading.
Is GMR Airports IV high today?
The top of this page compares GMR Airports's IV (at-the-money IV) with its last 20 days' actual move and with its own past. IV well above HV, or an IV percentile above 80, means options are expensive; IV below HV or a percentile under 20 means they are cheap.
Why is IV usually above HV?
Option sellers take on the risk of a sudden big move, so they ask for a little more than the movement they expect. That extra is why IV has been above the move that followed on most days, and why selling options pays on average but loses heavily when a big move comes.
How often is this updated?
IV updates through the trading day; HV uses daily closes and changes once a day. The F&O stock table uses each stock's at-the-money options for the current month.