A temporary hit point, like a hit point, is an abstract measure of how far a character is from dying as a result of damage. Temporary hit points may be granted from feats, powers, or other effects.
Differences from hit points[]
There are several rules differences between temporary hit points and hit points.
No stacking[]
Temporary hit points stack with hit points, but never stack with new temporary hit points. If a character already has temporary hit points and receives new temporary hit points, the character keeps either the current amount or the new amount. For example, if a character with 6 temporary hit points receives 4 temporary hit points, the character will still have 6 temporary hit points. If the character then receives 8 temporary hit points, the character will then have 8 temporary hit points.
Not healing[]
Gaining temporary hit points is not healing. Temporary hit points are not added to hit points, but tallied separately, and do not affect rules that depend on hit points, such as the bloodied condition.
For example, a bloodied character who uses the heroic effort warlord utility power, gaining temporary hit points, remains bloodied and continues to let allies deal bonus damage, regardless of the amount of temporary hit points gained.
Removal before hit points[]
Damage removes temporary hit points before hit points. For example, if a character with 6 temporary hit points takes 4 damage, the character loses 4 of the temporary hit points, and no hit points. If the character takes 4 more damage, the character loses the remaining 2 temporary hit points, and 2 hit points.
No penalty at 0[]
When a character's hit points reach 0, the character falls prone, unconscious and dying. When a character's temporary hit points reach 0, however, the character experiences no additional ill effects.
Expiration upon rest[]
Temporary hit points expire upon a short or extended rest.