May 18, 2019 at 7:48 PM #122905
There is only subtraction used in this analysis.
You need to understand the logic behind it, What does Premium Decay mean.
I suggest try to prepare that excel sheet by your own, then you will be able to relate it, which Premium is decayed on concerned strike price.
On some bad day it may confuse you, but believe me its not Rocket Science. Its simple logic.