I'm programming a tool to help with monster building. I'm leaning a lot on the angry GM
The features Undead Fortitude and Relentless adjust HP by a static amount. As I am calculating defensive CR, I'd like to factor that HP bump into the CR calculation. Since HP at each tier of CR is given as a range, I'm curious how others would handle that calculation.
I'm sorry if I get some of the below numbers wrong, I don't have my books right now
A CR 4 monster has 116-132 HP. These traits above increase HP by 7[ish] at this level. Adding 7 to 116 HP is still a CR 4 monster. Adding 7 to 132 is a CR 5.
The only way I can think to resolve this is to decide starting defensive CR and monster size, calculate hit dice and what the average HP would be for that CR and that monster size, then apply the trait bonus and see if that HP increase bumps the monster into the next level of CR.