*snip*
Next you calculate the monsters DPR which gives you the "expected Attack CR," from the table. This is then adjusted by the attack bonus and traits to give you the Attack CR. These are then averaged to give you the Final CR (which may cause adjustment to proficiency bonuses). That is how I like to work. Your spreadsheet attacks it a little differently that is all. No worries.
Thank you for the quick response and hard work!
Except the Attack Bonus and Save DC are both modified by the proficiency bonus, which is set by CR for a monster and need to be in place before the final CR is calculated. If it makes you feel better, just think of it as "Proficiency Bonus" instead of "Expected CR" as the only actual effect that "Expected CR has is to set the proficiency bonus in the rest of the sheet. All the other information that it sets is advisory only. So you can set it to any of the following values:[table="width: 100"]
[tr]
[td]Proficiency Bonus[/td]
[td]CR Range[/td]
[/tr]
[tr]
[td]2[/td]
[td]1-4[/td]
[/tr]
[tr]
[td]3[/td]
[td]5-8[/td]
[/tr]
[tr]
[td]4[/td]
[td]9-12[/td]
[/tr]
[tr]
[td]5[/td]
[td]13-16[/td]
[/tr]
[tr]
[td]6[/td]
[td]17-20[/td]
[/tr]
[tr]
[td]7[/td]
[td]21-24[/td]
[/tr]
[tr]
[td]8[/td]
[td]25-28[/td]
[/tr]
[tr]
[td]9[/td]
[td]29-30[/td]
[/tr]
[/table]
And I understand what you mean about not wanting to decide on a CR ahead of time. You can also give the Attack Bonus and Save DC a fixed modifier to simulate the proficiency bonus, but you may need to double check at the end that the monster's CR and proficiency bonus line up if that is important to you.
When I made this tool, I was converting a lot of monsters from 3.5 to 5e for my Age of Worms campaign. I used the Encounter Level of the encounters in the campaign as a guide and set the encounters in the 5e version as medium encounters for a group of 4 PCs of that level. So I knew how many monsters of a certain CR that I wanted. The HP and DPR ranges were more important for me to quickly ballpark the monsters in to a given CR before their special abilities adjusted the effective HP, AC, DPR, attack bonus, and Save DC.