# Converting Historical Volatility to Implied Move

I am trying to calculate an implied one-day move value for an instrument given its historical volatility. While I am familiar with this formula for implied volatility to implied move:

and intuition suggests this formula would hold true also for historical volatility, I am given pause by the often large difference between the two. I am obtaining historical volatility from TradingView and thinkorswim, both of which use the formula and methodologies outlined in the thinkorswim link.

I am aware that historical volatility is backwards looking, but I am simply trying to calculate the expected move over a given period of time if volatility were to remain at the historical value.

In short, I am seeking assurance in the validity of using historical instead of implied volatility in the formula pictured above. And if one wishes, perhaps an explanation of (or resource on) this often glaring difference between the two? Thank you all.

• Are you familiar with the $\mathbb{P}$ and $\mathbb{Q}$ worlds? – Bob Jansen Mar 31 at 7:42
• @BobJansen Sorry, I don't believe so. – Leafthecat Mar 31 at 14:30