> In my example this is roughly due to the time between now and the exercise date. Over time, this shrinks, this is called beta-decay. I think you mean theta d

> In my example this is roughly due to the time between now and the exercise date. Over time, this shrinks, this is called beta-decay. I think you mean theta decay. Theta is the time factor of an option's value. Beta is, roughly, a comparison of a security's (or portfolio's) volatility versus market vol. https://www.investopedia.com/terms/b/beta.asp https://www.investopedia.com/terms/b/beta.asp Beta decay is studied in a completely different industry. https://en.wikipedia.org/wiki/Beta_decay https://en.wikipedia.org/wiki/Beta_decay