Determining CR

[Yomega]

Hello everyone I hit a new stumbling block today and Im hoping you all have the answer I need.

Basicly Im trying to get away from relying on generators for my monsters without actualy understanding how it works.

I have 3 monsters from the mm5 I want to advance there hit dice to make them an apropriate challange but I am unsure how much to increase there cr as to give out a fair amount if xp and treasure I can post the actual monsters and where I want there hit dice to be but Im pretty sure mm5 isnt ogl so I dont want to break the rules.

Any help would be great thanks.

[Khedrac]

Urpriest's Monster Guide (http://www.giantitp.com/forums/showthread.php?t=207928) is an excellent look at how to advance monsters properly and I think it includes CR so it well worth a visit.

Aside from that the Monster Manual appendix on advancing monsters tells you how many hit dice it takes to add one CR by type - different types are different HD per CR.

[mattie_p]

Couple of notes, which are covered in the linked handbook, but posted here so you don't have to hunt too hard (do read the handbook, though).

Increasing hit dice (http://www.d20srd.org/srd/improvingMonsters.htm#increasingHitDice) improves BAB, saves, skill points, and adds feats. It may also increase size. See the same link (just scroll down a bit) for things that change with size.

It increases the CR (http://www.d20srd.org/srd/improvingMonsters.htm#addingHitDice). That table will show you how much to change the CR based on the hit dice you add.

[docnessuno]

The CR for advancing monster should be taken with a grain of salt.

A classic example is a hill giant with 11 cleric levels (non-associated), by the rules the total CR would be 12, despite the fact the resulting monster would have a whopping 21 HDs, with pretty relevant spellcasting and access to epic feats.

Use the rules for advancing monsters as guidelines, but always double check the results and ask yourself "Is this a balanced CR X encounter?", then adjust the final CR up or down.

[nedz]

Get a dartboard
Close eyes
Throw dart
The score is your monster's CR

Well that's how WotC seemed to do it.