Program won’t use 100% CPU

I have a PC that will not use 100% of its own cpu. I have a giant excell spreadsheet (over 20MB) and when I cause it to re-calculate itself(F9) or ask it to “save”, it will only use about 20-30% of the cpu max (this according to task manager). I have documented this with the spreadsheet being the only application open. How can I unleash the power of my PC so that I don’t have to wait forever for this thing?
thank you in advance for any help you may be able to give me.