Quote Originally Posted by Sporeegg View Post
It gets calculated the same as the Con bonus from rage. The main point is avoiding the "sudden death syndrome" induced by dropping under 0 while raging and suddenly loosing 2/3/4 * level HP due to falling out of rage.

Your average Con 16 -> Con 20 Barbarian on 3rd level looses 2 * 3 = 6 HP and if he drops to -5 before rage ends, you are effectively at -11.

Later on, your Con 18 (belted) -> Con 24 Barbarian on 11th level looses 3 * 11 = 33 HP. So when he falls unconscious on -1 HP, he immediately looses 33 HP, pushing him to -34 and killing him.
Basically. The constitution boost is a trap.