How to Compute CR For Human NPCs

What's the formula for computing CR for humans, elves, dwarfs etc that includes even the NPC classes like warrior as well as fighter, rogue etc.?

thanks

If a zero-HD being has PC class levels, then CR = total class level -1.
If there are NPC class levels involved, then CR = total class level -2.

If a zero-HD being has PC class levels, then CR = total class level -1.

If there are NPC class levels involved, then CR = total class level -2.

so how about these

warrior 1 = 1/2
warrior 1/rogue 1 = 1
rogue 1 = 1/2
rogue 3/fighter 4 = 6

Actually, it's CR-2 if there are ONLY NPC class levels, so it goes like this:

warrior 1 = 1/3
warrior 1/rogue 1 = 1
rogue 1 = 1/2
rogue 3 /figher 4 = 6

Actually, it's CR-2 if there are ONLY NPC class levels, so it goes like this:

warrior 1 = 1/3
warrior 1/rogue 1 = 1
rogue 1 = 1/2
rogue 3 /figher 4 = 6

and prestige classes, like core classes?

Yupps.